The biggest problem you have as an older guy is figuring out how to give a young girl an experience that fulfills her at her level. Whenever I see guys talk about how if you want to get younger girls you have to look exceptional or put in some huge amount of 'work' on yourself, as if they are these femme fatales with sky high expectations, I know this guy is scrabbling in the dark.
As you get older in life the problem is that you get jaded, serious, unplayful, logical, you get an end-of-history illusion about your own life and its possibilities. It's difficult to find things that surprise you, pique your curiosity, arouse your imagination and fill you with a fullness of yourself. You've got a career, you've got a routine, responsibilities, etc, and that's probably how it will be until you get shovelled into a retirement home and die. And when you wear this on your face and in the hunch of your back, this makes you boring and uninteresting for a young girl who is still figuring out who she is.
As Carl Jung said the most important task as you age is to maintain you inner child, to not let it get crushed by the repetitive mundaneness of a life that has stopped growing and changing.
Even worse is when someone has aged ungracefully (not physically but spiritually). That is when they feel unfulfilled and confused by who they have calcified into, and stuck in it, and are emotionally triggered by the spontaneity and naivete of those much younger than themselves, attributing all sorts of untoward motivations and strange perspectives on them to explain the reactions they provoke.
Nothing creates more of a sense of repulsion in a younger person than seeing an older one who cannot feel comfortable around them - you are expected to be more than them, to know more and to have experienced more of what that person is excited to become, to feel at ease with who you are around them - for what does this young person yet know about anything?
If you are with a girl who is much younger than you, you simply have to express that part of you which is at her level. A more reckless, playful, spontaneous, open-minded, dont-give-a-fuck side of you. So that you share an experience of the world in which you can connect emotionally and physically. Otherwise you will always be on the other side of a wall made up of days and months and years, and she will not be able to connect with you or arouse herself with you.
If you don't have a side to yourself of that kind, then that is your problem.
Think of yourself when you were younger - what sorts of older people did you really enjoy and look forward to spending time with? No doubt it was the ones who were the most light-hearted, unserious, ready to have fun and get up to no good, unselfconscious individuals. The rest you just looked at as wallpaper, boring with nothing to offer. Well, why are you not that person, if you admired them so much? Who did you become instead?
The key to connecting with someone is always along the path of truthfully understanding how they experience the world, free of the interference of your illusions and insecurities. Don't get run into the ditch by some negative inner voice with crude explanations of why younger girls don't like you.