Adult child's individual tax return

Hello,

 

I have an adult child (19) and he is in college. I have been claiming him as a dependent on my tax return (married filing jointly using Turbotax Home & Biz). This year starting in summer, he is starting part time work (W2) and might continue this work over fall and winter too. However, that earnings will not be enough for him to on his own (i.e. still dependent on me).

 

At what point in time, he has to file his own taxes and I stop claiming him as a dependent on my tax return?

 

Also, can he contribute max to his Roth IRA even if his income is less (e.g. his earnings in 2021 is $5000, can he still contribute $6000 to his Roth IRA)?