Ok i have had experience with this.
I had a b e a u t i f u l girlfriend and after about 3 years I kinda lost that drive. I thought it was just me being bored with her......boy was i wrong!!!!
I quit smoking pot(any drug fits here) and started working out.
Let me tell you, I would hump a tree if it gave me a wink..haha jkjk.
But really, compared to how I felt when I was a stoner and a lump on a log, having the sex drive back is AWESOME! Go out there, flex those muscles, pump some iron, let the sweat flow and you wont have any problems. But im only 22, dunno about at 80, id worry about breaking a hip or something lol.