yeah that always seemed a weird twist to have them grown adults in one universe but young teens in another. And how does that work for twilight when she jumps between worlds?
My headcanon is that Equestria Girls is pony-created fiction. Think about it: humans having technicolor skin makes no sense from a human perspective, but makes perfect sense from the perspective of a technicolor pony imagining a human world.
male characters with a strong level of masculinity are relegated to being either extremely evil or antagonistic (Sombra, Tirak, Iron will), being incredibly stupid or damselish (Bulk Bicep, Shining Armor) or just having little to no characterization from a few lines (Big Mac).
Now its had a lot of one shot male characters showing a variety, and of course you have ones like discord, whos still the best character on the show, but outside of him, all the other main stay male characters are just lacking in character or presentation.
Yeah, that bugs me, too. Though I haven't seen the latest episodes, so they might've corrected that flaw and I just don't know about it yet. Hopefully, someday either the main show or spinoff will be properly co-ed.