They used to have no limit on birthday guesses, but now you only have 3 tries per day
Ive lost more than one older account because I didnt like putting in my real birthday either.
If you can, create/use another account and neofriend the one you cant get into. That'll show you your age, and let you figure out what birthyear you put in. From there, you just have 366 days or so to choose from. Maybe you used your real month of birth with a different date. Or a different month with the same date. Sometimes people use holidays or have dates that they'd use over others, and so on. Good luck getting into it again.