Eh, he might really be happy, who are any of us to say differently. In the end he has to figure stuff out. And if she is the one, crazy eyes and all, then good for him.
I got married 5 months after returning from my mission. Married like the 3rd person I had ever dated seriously, no experience with nothing except a single year away at college in Phoenix. 21 years old, she was 23, met on our missions. The stuff of fairy tales for the mormon world. We had no ****ing clue who we were or what we really wanted. Now married over 32 years, 4 kids, 2 GKs. I wouldn't change a single thing, except maybe wait a bit longer to have kids (1st kid born 1 month to the day before our first anniversary). Sometimes you don't find yourself as much as make a life for yourself. Actively choosing is better than wandering around and hoping for the best. In the end it is all a series of choices. As long as you recognize that and can accept, live with, and hopefully be happy with, the consequences of your choices, that is all that matters in this life. Not one of my kids went the way we expected or hoped, but they are all well-adjusted, generally happy and self-sufficient adults. That is all we could hope for on that front too.
Hopefully Flip is happy in his situation and can make the best of it, if that is what he chooses. Hell my first big crush was 4 years older than me, when I was 13-15 and I was convinced we would get married. And when I turned 15 we dated for half a year or so, seemed like forever at that age. I thought that was it, we were destined to be together, but she was going away to college, then she went on a mission. So that fell apart then. My 2nd was almost the exact opposite, 3 years younger when I was 17 and she was 14. We were inseparable for 2 years, and she was genuinely who I thought I would marry before I met my current wife. Hell the whole ward thought we were destined to marry. It was actually kind of a big shock for a lot of people that we didn't. But at those ages you have no idea what love is, how it feels, and you fall deep and hard for the ones you love. It doesn't mean it cannot transform into something real and long-lasting. To this day I cannot tell you why I ended up with my current wife, but I am very happy I did. And even then, at 21, I had no clue what love really was or what it took to hold a marriage together. But we learned, and worked at it, and, well, so far, so good.
If something comes out that shows grooming when he was 15 beyond just a couple of young people falling in love, despite the age difference, then that might be different. In the meantime, if he is happy with it, and she is happy with it, that is all that matters and we really can't say **** about it.