Age has very little to do with maturity. There is also a serious power imbalance with every LI in this story, what makes Gabby any different just because she is 18? Idiot thinking, usually from people in the States who tend to have an issue with what other people do and who they date and think anything more than a 2 year age gap is weird (regardless of any 'perceived' power imbalances).
I diagree, age has a substantial effect on maturity. There's certainly variation within any given age bracket and plenty of overalp across ages, but the center of the maturity bell curve goes up with age. There really is no substitute for experience and the younger you are the less time you've had to experience new situations.
Gabby exacerbates that issue because she's already on the lower half of her particular curve. Neon pointed out her physical traits and domestic situation, which is certainly valid, but I think it runs deeper than that. Gabby
acts like a child. She rebels against her stepmother, she lashes out whenever anyone defies her, and she absolutely refuses admit her real feelings - even to herself. And of course her childish behavior results in people continuing to
treat her like a child, which only intensifies her frustration causing her to lash out even farther. I'd argue it's only in the previous update (where she mutes her normal hair color before going to see her father in jail) that she finally shows signs of the adult she's growing into.
This is obviously not to say Gabby is a kid or that her portrayal is flawed, just that I think there are very good reasons to treat the MC romancing her with a more skeptical eye than most of the other LIs despite their similar financial issues.
