What's the average strength of a 17 year-old male?

Well, the average strength depends on a variety of variables. Say this boy works out pretty often -- in that case, his strength may be double than the next man over. However, a boy who is active but not to the point that he is overtly muscular can probably heft a 75lb - 100lb item around for a few minutes before his body begins to ache. The maximum, I'd say, is about 120lbs.