Post Malone was 21 in Seth Rogen's Hilarity for Charity when he played the character 'Himself'.
That was over 6 years ago in 2018.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 28, and has starred in 13 movies in total, 10 of those since Seth Rogen's Hilarity for Charity was released.
In Seth Rogen's Hilarity for Charity, I think Post Malone looks: