depends on his interests. Usually I think of samplers having a variety of stitches or alphabet. If you are not looking for a traditional sampler, I would consider nature, cars, or farm choices. I did a piece for my son that was a Coke Santa (he likes Coke Cola). I like the look of fractals too.

Curious -- are you looking for a sampler to stitch for your son who is a mature man? Or are you looking for a sampler for your mature son to stitch.