Should I think about it?

Age means nothing. Forget this person as her comment to you was moronic and ignorant. As long as your horse is healthy and sound and enjoying his work, you should not just retire him. Because of horses receiving excellent care and nutrition, etc., they are working much much longer now without issues. It is good you are not jumping him too much but as long as he tolerates it well, there is no cause for concern. Even if a horse has some arthritis, as long as it is not debilitating, riding him is good for him. The more he moves, the more he will be able to move. Again, sounds like this guy has a great life and he has not problems so you should absolutely enjoy him and he likely has many more years to come. My WB eventer turned 22 last August and he is wonderful. We don't compete anymore but we still get out and ride our maneuvers and he loves it as he is a "professional". I don't ask him to do anything over strenuous, but he loves his work. Again, just ignore this person as she doesn't know what she is talking about. A friend of mine has a 35 year old quarter horse that still goes on trail rides. Please. It is not a matter of the numbers. Take care and enjoy your horse. He will tell you if he can't do it anymore.