I don’t know if it is an age thing. Personally, it is hard to make me cum from oral. That has always been the case, even when I was young. To be honest, only one woman has ever really made me cum whenever she really puts her mind to it, even to the point that I will almost curl up because the sensation is just too overwhelming. #orange-sky-forever
To get to help with your issue, I’d say the following things: (a) always, (meaning never stop), keep the shaft going; (b) lots of thick spit; c) spend time on the tip as well as deepthroat; and (d) eye contact.
Most importantly, the shaft. Basically, see blowjobs more like “handjobs with assistance”. If he can make himself cum from his own hand, then you are home free. Give him a “handjob”, and assist with the mouth and eyes.