How is it wrong? You said they knew each other til he was 9, then had no contact at all.
So he was 9, she was 18/19, and there was absolutely no attraction there then, it is in no way like you're trying to sensationalise it to be like "She's known him since he was a kid" because she had no interest in him as a child or young teen, they werent even in contact.
Everyone is different, some 18 year olds are more mature than some 30 year olds, and BOTH are consenting adults. It is also completely possible to have mutual interests and just "click" with someone, regardless of age gap.
At 18 i started dating a 21 year old, he was selfish, abusive and self centered and whilst he was posh speaking with big words, he wasn't mature at all. college drop out, refused to work, wanted money not a job, parents did all his washing, cooking etc. A week after i turned 22 i met a man (something i refuse to ever refer to my ex as)who had turned 17 a month prior, and he was incredibly mature, way beyond his years. Full time college, part time job after work, had already passed CBT to drive motorbike, taking driving lessons, did his own washing, cooking etc, not as intelligent as ex but far, far more grown up and responsible. We had loads in common, not just interests but outlook on life, and he stood by me through the worst year of my life when my illness rippled me. 5 and a half years on im 27 hes 22 and we get on as well today as we did the day we met, still got same outlook, same goals etc.
Ok thats a just shy of 5 year gap not almost 10, but it categorically is NOT an adult and child etc situation, 16 or over (in the uk, and once finished at school) there is nothing illegal or "wrong" about there being an age gap.
Angelina Jolie was 12 years younger than Brad Pitt, was that wrong? As long as both parties are adults with similar wants/goals theres no reason at all it can't work out.