Jensen Ackles was 18 in Alien Resurrection when he played the character 'Dead Soldier (uncredited)'.
That was over 26 years ago in 1997.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 45, and has starred in 13 movies in total, 10 of those since Alien Resurrection was released.
In Alien Resurrection, I think Jensen Ackles looks: