OP: You're being disingenuous from the get go. Surely you know how many men and women are hood-winked by disingenuous people when online dating. Whether you intend to confess right away or not, your profile is false and I'm sure these men are wondering what eles you're capable of lying about. It is indeed a red flag.
You ask what you should do. If you want to attract men who are younger than you and you're afraid that your self proclaimed youthful good looks isn't enough bait to hook someone then at least put right in your profile your real age and your reasons for using a younger age for coming up in searches.
I would also think that younger men looking for cougars wouldn't exclude a 40 year old that is in good shape and has an intriguing profile however don't expect them to be serious about their intentions. I'd venture to say that the majority of them are just out fishing in a barrel.
Good luck
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion