Two things ; worrying about your age is a handicap you don't need .I am 81 going on 82 I may not be as fast or as energetic as the younger group but I took 3 deer in the county and 3 in the suburban hunt this year so may be you could plan on being around a while.
The other thing is safety first beginners often get damaged fingers or ruin a bow by shooting with out an arrow loaded.
There are a lot of good xbows out there be sure to shoot before you buy a good trigger pull is necessary for offhand accuracy, a strait bow is tougher and easy to maintain but may be a bit slower. If you plan to hunt from a tree stand and get shots at 25 yards or less a xbow in the 300 fps is more than you really need.