Dhanush was 17 in Thulluvadho Ilamai when he played the character 'Mahesh'.
That was over 22 years ago in 2002.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 40, and has starred in 54 movies in total, 51 of those since Thulluvadho Ilamai was released.
In Thulluvadho Ilamai, I think Dhanush looks: