Is it better for my 21 year old son to file separate taxes this year, He isn’t in college any more, he does still live with me, he has a part time job for 7 months?

[Opus 17]

A child, even if they are a dependent, must always report income earned from working on a tax return in their own name.  This, by itself, does not change the calculation of whether they might be a dependent of their parents or someone else.

In your case, because he is 19 or older, you can only claim him if he was a full time student for at least part of 5 different months in 2017 (such as, the Jan 15- May 15 semester); or if he was not a student but his income was less than $4050.