I never had it and I'm 29. Had the vaccination at about age 16, then had a blood test a couple of years ago which showed I wasn't immune. I'd been exposed heaps of times through work though, so not sure why I never caught it! Anyway before ttc I got the vaccination again, twice. Not sure if I am immune as I haven't had a blood test to check since, but I figure if I'm not now after having the vax twice then I never will be.