Idk what's wrong about the age gap if in the end they're both single, both without children prior to reuniting, both with stable income, and both smart enough to not fuck up each other's lives.
The age gap would only be "weird" if any of those conditions I stated, or probably some other details...
Ofc a 16 yr old girl wanting to marry a 40 yr old man is normal in this fictional setting.
Stop comparing this fictional world's common sense and morals to present, real world ones.
If sex or gender is your problem, it's not supposed to be since the character's sexes are very easily...