I strongly agree with BigAllOver. Get a personal trainer if you can, but make sure the trainer is a good one.
My understanding is that you should take 48 hours rest before working out the same muscle group again (for the bigger muscle groups). My trainer told me that if you really want to grow, you should work out the same (bigger) muscle group within 72 hours. Smaller muscle groups (arms, abs) require much less rest. I've never read anything to indicate that age is a factor.
Of course, as was posted already, you should really just try different things and figure out what works best for you. Everyone is different, and everyone's body responds differently.