Most everything dwindles with age, perhaps power lasts longest. Good defense requires speed and a good throwing arm in the outfield. Ty Cobb focused on getting on base over power. Hank Aaron was usually slotted just below Mays though he had a bit more power and good speed, he wasn't as elite on defense.
I don't know who has the worst arm in MLB now, but it would still be quite a good arm in a relative sense. Maybe you can play 1B if you have a particularly average arm and otherwise are very good. Even second basemen can throw 85 mph or so, which is WAY above what most HS pitchers can manage. A pretty good HS pitcher can throw around 70 mph. If course, some can really bring it, but they are rare.