Could it not be called an ageist abuse, to convince someone who is now older, that they are somehow "damaged goods" for engaging in activity they were consenting to when younger?
I mean, there's a super long list of things that people change their views about doing according to their current age. If you believe the other person was willingly taking advantage of you just to get something they wanted due to the limits of your knowledge at the time, then yeah, why wouldn't you feel negative emotions and betrayal?
However, this "taking advantage" mindset is not automatic simply due to age difference alone. To claim sincerity by the older partner is outright rebellion to many self-proclaimed child advocates, but it is nevertheless quite true in many instances. So why subject the young partner to a lifetime of believing they are damaged and can no longer trust anyone at all, when it just might be that the older partner truly believed in the love they experienced just as much, even if the younger one comes to believe that partner was mistaken later?
Imposing a belief on society is common, but it begs discussion when it also requires some people to endure a lifetime of shame and pain.