How old was Michael Jackson when he did billie jean?

The song "Billie Jean" was written in 1981 because on the "Thriller 25th Anniversary Deluxe Edition" album on there is the song " Billie Jean ( Home Demo from 1981 ). But the version on the song "Billie Jean " we all come to know & love today was created in 1982 for the "Thriller" album. And another version of the song " Billie Jean " is: "Billie Jean ( Long Version) which is 6 minutes & 23 seconds & is on the "Thriller 25th Anniversary Zombie Cover ".