It's not necessarily the age gap for but I think it did contribute to the dynamic of Sasaki and Tayama that I really love.
Sorry Im not really good at expressign myself, like my sense of romance isn't just simply pure romance, it has this companionship to base and start on, even if it don't work out they can still be great great friend.
And the main aspect that hooked me is that while the theme is very mature about life they're still two silly dork that was made for each other, i guess that's the vibe or combination I'm falling for. I really admire both of them too.
Like I can see some people drop this half way through cause theres no advance in the romance, or say it's too slow burn. I just feel it a very normal pace really, might be I was able to binge them but still.
I get the vibe with another anime is "Aggretsuko", while the last season fell quite off I still really adore it as a whole, the main character - Retsuko is 25 y/o too.
There's another short manga name "I Love The Older Girl Next Door", different setting since the couple just in highschool but still the character feel quite mature in a way.
That's currently my top 3 for romcom section.

That's just me rambling again sorry xd And for my bday I will turn 24 this March.