Even though my son made over $4300 in 2020 he was a full time student and I paid all his living expenses why can I not claim has as a dependent?

In order to be a qualifying child, the person must:  

• Be your son, daughter, stepchild, foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, or a descendant of any of them 

• Be under age 19 or under age 24 and a student for at least 5 months during the year OR permanently and totally disabled 

• Have lived with you for more than half of the year 

• Not have provided more than half of his or her own support 

• Not be filing a joint return for the year 

Is he under age 24 as of December 31, 2020?  Amount earned isn't relevant unless he is 24 or older. 

Rules for Claiming a Dependent  on your taxes.