They might as well.  66 is the new 56, you know.  Honestly, though, some 66 year olds still have great bodies (my mom is in amazing shape).  As far as being tasteful, I would guess it would depend on what the shirt said...if it was something like "porn star" or "bootilicious", then that's tacky on anyone.  But any other fitted printed tee should be fine (as long as there's no boobs hanging out of it or excessive midriff...again, not really tasteful for anyone).