I'd say it's pretty common. When I was younger (in my 20s and 30s) I loved much older guys but as Ive got older, the age of the guys has gone the other way and I now like younger guys. It doesn't mean I write off all the more mature guys but as a general rule I prefer younger.
In any case it's probably a good job I'm not still into much older guys, as at my age, I'd have to dig them up and necrophilia is one kink I'm not looking to get into lol xx