As im getting older its only happened 3 times that i can remember but its becoming hard to get hard on demand...should i be worried?

ED: A very large percentage of men experience occasional episodes of erectile dysfunction by the time they reach 40. Causes, especially in younger men, include fatigue, stress, drinking too much alcohol; as men age chronic diseases like diabetes and taking medications contribute many more cases. Work on lifestyle: good sleep, stress control, watch alcohol, exercise. If increases, see Doc. Rx available

See answer: If you are able to get a full erection when masturbating or on awakening in the morning it's unlikely a physical problem. If you get a full erection but unable to maintain it you may have a venous leak. If unable to get an erection you may have low T or another problem. See: http://bit.ly/1wHjFsh and http://bit.ly/1IKyqJV