Why can't I handle hunger like I could when I was younger?

I’ve always been tall and slender. Some would say that at 5’8” and about 120 I was underweight. I don’t think I was. I was an athlete and in great shape.
Eating has always been a low priority to me. I eat because I have to.
When I was younger and I got hungry I could just ignore it and it would go away for a few hours, then come back stronger and so I’d eat a bit just to make the hunger go away. On more than one occasion I’d go to bed at night and suddenly realize I’d forgotten to eat anything that day!
Once, as kind of a competition with a friend, I went 5 days without eating. Wasn’t that hard, either.
Ever since I hit about 45 years old, though, it’s different. I get hungry to the point of screaming ravenous. I can’t ignore it any more. It’s like I’ll start trembling and get dizzy with hunger.

What changed and why?