My Husband (67 Y/o) Exercises Strenously And Regularly, Both Cardio

My husband (67 y/o) exercises strenously and regularly, both cardio and weights, eats very healthy yet is gaining weight. He also is fatigued no matter how much sleep he gets and is getting regular sever headaches. We had his thyroid test and it came back normal. He's getting very frustrated and doesn't know what else to look for. His Dr said it's probably just age, we're not buying that. Any suggestions?