Gabriel Byrne was 27 in On a Paving Stone Mounted when he played an uncredited character.
That was over 45 years ago in 1978.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 74, and has starred in 104 movies in total, 99 of those since On a Paving Stone Mounted was released.
In On a Paving Stone Mounted, I think Gabriel Byrne looks: