The 42 year old new hire at your job confesses to you that he has had 48 different jobs in his life. What is your opinion on that?

By that age, I was into my third long-term job (> 5 years) and had had upwards of 16 short term ones - multiple part time ones at once, or some just for a few weeks or a couple of months here and there between the long-term ones etc.

48 doesn't seem that unlikely - nor even an indicator that they will not be staying put for any length of time unless your job is a shitty one with a high turnover anyway.