If you are getting older and slipping in energy, you might have a simple vitamin deficiency.
Researchers recently followed 698 randomly selected Italians over 65. They found low vitamin E levels associated with reduced physical performance. Of several micronutrients tested, only low levels of vitamin E stood out.
If you are losing energy, ask your doctor to test your vitamin E levels. You should have more than 1.1 mcg/ML. If you are low, this is a time you really need a supplement. My favorite brands of vitamin E are Unique E and Carlsons E. I see no risk in a supplemental dose of 400 IU per day.
Ref: JAMA, 2008; 299(3): 308-15.