A dad asked me about a starter bike for his slim 6'3" son -- something good to just get out and ride for a couple of hours. I think he'd be equally well-served by a road or mountain bike (or something in between). Probably prefer 29-er if MTB, but I don't think he's too choosy.
Maybe looking for that bike you set aside a while ago but still has some life in it.
James Claus