For my comic on tapas, my characters are in college, so they are all about 18 right now. (Yu-Jin is older, but only a bit, so she's 19 or 20, I think).
Original fiction that I've been working on and haven't posted anywhere, my characters are:
Dragon's Lament (high fantasy) - 21, 21, 43, 25, 30ish
Cat's Eye Blind (urban fantasy) - 27ish, 27ish, 30ish, 150-200ish (he's a vampire).
Fairy Lights Inn (romance) and Fairy Island (lgbt+ romance) series - each story has a different main couple to get together who range in age. The unifying factor are three elderly women who open a bed and breakfast (the Fairy Lights Inn) on Fairy Island. They are, subtextually, retired fairy godmothers who can't help meddling by bringing compatible people together and giving them a chance at love.
There's definitely a convention, or trope situation where fantasy and romance genres seem to expect a young adult main character, when I think about traditional published fiction that I've read. Mystery seems to have more main characters that are older.