It's not so much that people change…it's how others perceive them that changes. It's easy to crush on someone when you don't know them all that well. When you get to know them better, you find that the qualities that precipitated the crush were only illusory.
As to that whole "getting older" bit… I think your "type" does tend to change as you get older because you want to pair up with someone with interests you hold in common. I couldn't come out and say this then, but when I was still in college I was attracted to teenagers. As you get older, your options are a bit limited…you can't date underaged girls because you can get arrested if her dad doesn't like you. Deflowering an 18-year old college freshman becomes a sort of sport if you're into that. But in those years finding "the one" isn't quite as urgent as it is finding someone you can just have fun with, i.e. someone you can go drinking/dancing/bowling/movies with and maybe a little something extra besides if you catch my meaning. Girls just wanna have fun as much as guys do at that age. I'm in my mid-30s. So I'm less concerned with recreation and getting laid than I am being good at what I do and making a career out of my interests. At some point between 25-30 at the latest, you really do need to start making some babies, so if you are somehow single between 30-40, you're going to be more concerned with stability than anything else. In your 40s, you're more concerned with your kids than anything else. In your 50s, you're wrapping up your career and preparing for retirement/second career. You're not far off from grandkids by this point. Throughout your 60s-70s, you're just enjoying your hobbies, community activities, etc.
Let's say you're 75. After all this time, you FINALLY can afford to buy that electric train set you always wanted as a kid but never had the time or the money to work on. You've got an entire portable building dedicated to your trains. Explain to me exactly how a 19-year old college sophomore is going to find that attractive? All this guy ever does is sit on his front porch, whittle sticks, and play with his trains, I wanna go DANCING!! ! I wanna get drunk, but this guy has a heart condition…whut????
The widow next door, on the other hand, really just doesn't want to be alone. She spends her days with her cats and her knitting. So her only real interest in another person is keeping warm on a cold night and not having to eat breakfast by herself. She doesn't really care if a guy spends all day playing with trains and going fishing.
Obviously I'm exaggerating a little bit. But where you are in your timeline is going to have an effect on your interests. I'm a musician, been playing with a couple of bands, play in a church, teach piano lessons…I've got some good experience and think it's time to release my long-overdue first instrumental albums. I'm also a stay-at-home dad with three kids. If I were single and looking, I'd be interested in someone willing to partner with me for gigs and who probably already had kids of her own, or at least might be interested in having children if she didn't already. I'd be interested in someone with a good steady income who can support herself since I don't make a whole lot of money right now. And she'd have to be ok with the fact that I'm lucky to come up with enough money to take her out to dinner maybe once every other month. Not a lot of "normal" women can really handle that, but I'm also the kind of guy that will give most anyone a chance. If I'm ever able to make a lot of money, then this won't be an issue, and I certainly don't intend to stay poor for the rest of my life. But I have no illusions, either. And I don't see what a teenager could ever see in me at my age. I'm not saying it COULDN'T work out, but I doubt the likelihood that someone 18-19 would ever take a lasting interest in me. I'm not a sugardaddy, and I'm certainly not interested in a golddigger. Actually did briefly date one once. She had a heavy crush on me, but that wore off the longer we stayed together and when the money ran out. So…no, I'm not going back there. It's certainly OK if someone 18-21 showed a lasting interest in a 40yo, but most often the age difference brings disparate interests which spawns conflict. You really have to be careful with that.