How young can you be when you irrevocably mess up your life? and How?

If, when you're born, you don't choose to be rich, that messes you up forever.

If you're not born rich you can become rich (or "comfortable") later in life. It doesn't mess you up forever.
- And you become a successful businesswoman carrying a chocolate bar with her at all times because of your childhood fear of starvation. Sure, that doesn't sound messed up at all.
- No, sorry, we actually just sold out of upward mobility. Our next shipment comes in never though, maybe you can come back then?
- Oh gee, I hadn't thought of that. I'll go tell the African children. /s
  
  Just eyeballing the life stories I know, and looking at the actual statistics on social mobility, if you do everything right you can expect to climb up like a single rung of the socioeconomic ladder. On average. There's a great deal of luck involved there, even, and it's possible to do everything right and go down the ladder if, for example, something unexpected cripples you.
- Hey now, that sounds like a lot of work that'll get into the way of my doom scrolling and being a miserable bastard time

I was watching a Netflix documtary about killers, the guy said he was on drugs by age 9...so pretty sure that messed up his life before the murder. It is debatable on if surroundings or self choices are why you try drugs I guess.

It takes a certain kind of environment to enable that.
- Agreed. Also Nancy Reagan told me not to, and I was not in a position to argue.
- Right, "should I do drugs?" is not a typical choice for a 9 year old to have to make, they should be protected from that. I have heard stories of particularly shitty parents giving drugs to their own young children.
9 year olds don't have "self choice" to use drugs.

Evem adults most often don't have it. Addiction starts with trauma, often in mother's womb. If mother is under stress while pregnant, huge and long stress, child has much bigger chances to become an addict.

Any significant injury that results in paralysis would be a potential candidate. These become possible as soon as you become old enough to climb things like trees.

Diving head first into shallow water comes to mind
- Also: eating random slug you find on the street.
A kid in my class put his arm inside a... I don't remember if it was a lion or tiger cage back on the 70s before safety was a thing. Being armless isn't the end, but I bet he regretted that decision.
- There went all his hopes for an army career. No more pitching for the Mets. No more professional arm wrestling. No more rowing competitions, or stirring huge pots of gruel.
I can do you one better: decide to explore near that baby gate that got left open.

Playing with fireworks, firearms, or chemicals can be a solid way for anyone of any age to ruin their life.

But doesn’t that count as an accident? Kids who play with fireworks don’t cram a steel can full of black powder imagining how cool it would be to loose your fingers and eyes.
- Maybe kids are too short sighted to see the risk, but who says they don’t do that? Among the stupid things I did as a kid was try to turn any tube into a gun/cannon/firework mortar, and hold it in my hands to aim and launch. We even had the benefit of my grandfather losing a couple fingers as a cautionary tale, that we completely ignored. If something happened, could you really call that an accident?
  
  Or the time we were playing with fireworks …. In a barn full of dry hay? I don’t know how my grandfather let us live after that one
  
  ….. but there’s a threshold of stupidity where you really can’t call it an accident. I’m happy to have survived in one piece all too many bouts of stupidity but the adult me wouldn’t call it an accident if something happened

Being conceived by shitty people is more than enough to have a life arguably ruined permanently before it even began.

So much can happen to ruin a person's life at any stage, even pre-conception.

OP is asking about wrong/bad/poor choices etc, the last sentence of their post specifically says it's not about situations that are inflicted upon them.
- You're right; those were poor choices by the parents.
  
  Really, the question is more about "When do we stop attributing bad choices to the parent and start attributing them to the child?"
  
  Because babies and toddlers can make lots of stupid decisions.

You're never too young to die, so the saying goes.

I remember as a kid, I met these other kids that would drink from the side of the street. That sewer water was full of nasty including gas and oil runoff from the roads and who knows what else.

I also had an ex that would drink the chemicals under the sink as a tiny kid.

That's crazy... where did you grow up?
- Los angeles

Actually, the younger you fuck up, the worse are the consequences. A 13 year old go in a school fight, he is kicked out of school, has to go in another school further away, sleep less, see his grade fall down, and next year he'll be pushed to start an apprenticeship rather than high school.

A 31 one year old (otherwise a good citizen) does the same. He'll spend a night in police custody and at worst pays a fine (with a high probability that change are dropped because judges and prosecutor are busy)

I agree with your general point but I don't agree with your example because apprenticeship can still lead to stable employment and a fulfilling life
That's a very unusual example. If you're prepubescent you can get away with straight up murder in a lot of jurisdictions and basically go back to your life after a few years, of lots of therapy, and legal supervision.

Be born a woman in Afghanistan... come out the womb to "And that's when she knew she had fucked up."

I'm not certain if this is in the spirit of your question but even a murderer in the US has privileges denied to a lot of other people.

The most formatting event in everyone life nowadays, and the one most negatively impactful is being born poor, that is age zero.

Drugs at any age. Sure you can get clean but it takes a very pacific type of person to do that and there are more people who have failed then ones who have succeeded. I made the mistake of using drugs at a young age and it has destroyed my life beyond repair. If there are any young people reading this just remember it's not worth it. Trust me nobody hates drugs more then drugheads.

Any age? Sure someone can drug and rape a 5 year old. But even with 8 it's hard to get the cash for a proper addiction. You mind sharing about what age you fucked up to calibrate my compass?

In the end, this was about self inflicted damage. Not someone abusing you.
- Well, no one does date grape for fun. No one's addicted to date grape and it doesn't matter if you have the money as long as you have the taste for it. I started doing drugs at age 14. Things like weed, benadryl, LSD, glue and shooms. In the long run I shouldn't have done it but I will admit I do have some nostalgia for doing them with my old friends.

Being born homeless.

To be fair, OP is asking about bad/poor/wrong decisions, the last sentence of their post specifically says it's not about situations that are inflicted upon them. No one gets to choose where they are born.

Having success in sports, entertainment or anything that pays out real money. There's not a lot of happy stories about child stars.

what can a ten year old do(besides mass murder & accidents) that messes up their life so badly that it is unrecoverable?

kill their own parents (it's not technically mass murder until you've killed three people).

Growing up in a house with sa at any age. For me I raw dogged life for my adult years blocking it out but stuff catches up and can be catastrophic.

I feel that. I'm about to be 23 and now it's on my mind again for some reason and idk what to do.
What is SA?
- trigger warning
  
  sexual abuse

About -9 months, you did not let others pass.

Being born into a life of wage slavery and renting.

Thanks mom and dad.

Whatever the country's age of criminal conviction (typically 18). It's hard enough to get a job WITHOUT a criminal record.

Depending on the country and/or crime, a juvenile record will also prevent being able to work in certain jobs/industries.

A ten year old can rush out into the road and become paralyzed for life.

Young enough to sleep with your teacher

I know a guy who got himself into $15k of credit card debt by age 23, who also smokes a lot of weed and is currently unemployed with no meaningful credentials beyond a high school diploma. I don't talk to him anymore but I'm almost positive he'll be homeless the next time I do.