I grew up with O gauge Lionel, but saw the light and moved into HO. Was a fascinating hobby. Thoroughly enjoyed it at the time. Too many moves though and it found new homes amongst the younger extended family members. Think I still have an engine and couple of cars.
He just needs a bigger layout than crammed in one corner. What would look really good is a shelf all the way around the living room. :~D
I still have all my HO engines and cars around someplace... and the old Aurora slot cars set that was *also* more or less HO gauge. It was great because you could set up trains and slot cars on the same board and it all pretty much matched. Had many many hours of fun with that stuff.