When it comes to age gaps like this one it can be hard to look past the obvious issues of feeling like a young child was taken advantage of. However, this story has done a good job at not having any weird grooming going on.
Yes ML and MC met when the ML was only a kid but he was the one that confessed his feelings for the older MC. And it's not like the MC was immediately ok with the idea of even being with the ML since he was a child. The ML worked on their relationship keeping it friendly until he was of age but always letting his intentions be known.
MC never really actively encouraged the MLs behavior but he also didn't push him away. ML could have changed his mind at any time as he grew up and MC would have let it happen. It is obvious who drove this relationship and hey it works. They kept it respectful and demure and they are now adults and fully in love and its hard to see anything wrong with that.
Nooo I can't wait I love this goofy family and I want to see them knock the socks off this old man with their goofy intellect