David Keith was 23 in Are You in the House Alone? when he played the character 'Student'.
That was over 46 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 70, and has starred in 81 movies in total, 79 of those since Are You in the House Alone? was released.
In Are You in the House Alone?, I think David Keith looks: