(Your age)/2 + 7, rounded up. That's your floor. If you're 45, you shouldn't be hitting on anyone younger than 30. If you do, you're a creep.
The people who say things like this are the ones who tend to be the actual creeps. If they were in their 40's they would rail a smoking hot 25 year old without thinking twice if given the chance and they lust over them just the same as any other man but because of their jealousness or bitterness they hide behind a front of moral superiority. It's the same reason most "White Knights" are the creepiest of all. They aren't actually nice guys who love and respect women. Quite the opposite. They are only nice because it allows them to hang around in the friend zone with their delusions that something will happen while they do their creeping.
If a 25 year old woman wants to get down with an attractive respectful 40 year old their isn't a creepy thing in the world about that without anything extraordinary making it so.
I'll give you a hint. 99.9% of women you know in their 20's definitely have a 40-something guy they would let go to town on them if given the chance and I'd love to see you tell them that they are wrong and that you know better.