Leif Garrett was 6 in Bob & Carol & Ted & Alice when he played the character 'Jimmy Henderson'.
That was over 55 years ago in 1969.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 62, and has starred in 33 movies in total, 32 of those since Bob & Carol & Ted & Alice was released.
In Bob & Carol & Ted & Alice, I think Leif Garrett looks: