That is, without question, not always the case.
X2, for many reasons.
Old Guy, even if you don't have your TT any more you can always rent a cabin or trailer at many campgrounds. If sleeping in someone else's bed bothers you, bring a sleeping bag or your own sheets/blankets.
A couple of thoughts. Have you had a check-up recently? There could be factors affecting your energy level other than age. Do you exercise at all during non-RV season? As we get older our ability to "pick up where we left off" decreases. The key is to not stop completely. Have you suffered some sort of loss that you connect with RVing? Cause could be psychological as well as physiological. Maybe before you give up you should try figuring out of there are other factors involved.