I or my family does have dog a 3 year old mixed border collie. Is it to late to train him for something new?

Man, the only time it's too late to rain a dog is when it has dementia. Which sucks, not that they cease to be trainable, but that they get dementia; it isn't fucking fair.

All you have to do is find the right reward, and break down the desired behavior into steps combined with signals.

You want a dog to sit, as an example, you find their magic reward. For the example, let's stick with a food treat. You get the dog's attention, you give a gentle push on their rear while giving the signal and when they get a little lower, you give the reward. Easy peasy.

You expand that by extending how far into the sit they get before they get the reward. Most dogs, you can have responding to a verbal sit command in ten minutes, and they'll remember it for ages. Once they're responding to a verbal command at all, give another signal with it, like a finger moving from pointing at them, then down. That way, they'll be able to respond to visual signals as well, which is handy when there's a lot of noise and they need to obey a command for safety.

It doesn't even have to be a word or a gesture, you can do whistles, clicks, whatever. The key is that each command needs to be distinct, and short. Trying to say "hey dog, jump up into my arms" might eventually work, but it'll take longer.

Which leads into training to get them doing something like that. Easiest is when they already display a behavior, like jumping. They jump up, you say "good jump" and give them a treat. Eventually, you say jump and they do it. More importantly, if you switch to only rewarding them when you give the signal, they're less likely to jump in their own, which is nice when you want to stop a behavior.

All training is a variation of that, with complex behaviors needing to be broken down into small steps, like "sit", then "sit up" when you want them to raise their front end off the ground after sitting. If you want them to go get a beer from the fridge, you teach them what beer is by first teaching "touch", which is making contact with something on command, then having them touch a can and saying beer. Then you have them go to the kitchen. Then to the fridge. Then pull the rope, then get the beer out. Eventually, you chain the commands, and they learn to do it all when you tell them to "fetch me a beer". What's really fun is when you extend that and get them to bring one to whoever you point at, or to someone whose name they know. This example here isn't structured perfectly, it's just to give the idea.

Timing signal, behavior, and reward is the key to all of it. Works on humans too, btw.

But you never need to use negative reinforcement at all. To the contrary, doing so delays training, and makes it harder. All positive, all happy, all reward based. You can get the dumbest dog on the planet to follow basic commands with the right reward and some patience.

Now, food rewards tend to be the easiest. They're portable, they can be used almost anywhere, and most dogs respond to a treat enthusiastically. But our isn't the only possible reward, nor will it always be the magic reward for every dog. Sometimes play is the magic reward, sometimes it's praise or touch. But once you find the thing your dog wants the most, give it to them regularly and connect it to behaviors, and they'll learn fast.

My little girl? She was amazing. She was trained to go get a treat, bring it to you, give out to you, and wait until you gave it back before eating it. Took a week. But, if you said "go eat a treat", she would go, get one treat, bring it to where she could see you and then eat it. If you said to bring treats, she'd bring the bag and give it to you, prancing the entire way since she knew it was play/training time and she'd get lots of treats.

She knew the names of every toy she had. She would go to the box and bring whatever you asked for, then "clean up" at the end of a play session by taking all the toys to the box.

Which, that's going off topic, but I can't talk about dogs without thinking of her, and the two year date of when she was put down was not that far back, so I'm missing her extra hard lately. She was best girl. Fifteen years of love, and I hope the best girl or boy you're asking about brings your family just as much joy.