I don't know if someone told you this or you are just assuming you need less sleep as you get older, but this is a fallacy. While it's true that older humans have more trouble getting enough sleep, it is absolutely not true that they need less sleep. I say this not to antagonize you, but to suggest that if a doctor is telling you this, they are dismissing you, because to invest more energy with you on this eats their valuable time, and I hate to see that happen.