starfleet.com has a birth year estimate for Ezri that would make her 21 during season 7. I think that makes her too young. Usually a counseling program today is a 3-year graduate program following a 4-year bachelor's degree. That would have made her only 14 entering college! It has happened, but Ezri doesn't strike me as the amazing prodigy type. Even allowing for a degree to be entered early and waiving the final year of her training, I'd still say she's more like 23 or 24 during season 7. Compared to Jake, there's a huge difference in maturity between 20 and living in the same station with Dad vs. 23 and completed college and mostly completed a graduate program and living away from home for 5 to 6 years.
I didn't like the Ezri-Bashir pairing either. Bashir would have been quite a bit older. Memory Alpha estimates he was 35 in season 7. My estimate agrees: 4 years undergrad, 4 years med school and 3 years residency, if he started at 17 because he was gifted he was 28 during season 1, or 35 during season 7. He's really robbing the cradle. I suppose it's better than Serena, but that's a low bar. The chemistry seemed a bit forced too. Ezri seems patronizing about the games, I mean models, he makes and the combat-simulation holosuite programs. I'd give it about 6 months before she called it off, less if they were no longer on the same station. But I can see a really great scene of Bashir visiting O'Brien on Earth and them getting drunk together while Bashir unloaded about how sad it was.
The age difference in relationship was not what I was referring to, I believe if your an adult LEGALLY you can find love at any age in the adult spectrum. During the 7th season of DS9 war times, Ezri had stories dealing with older people most of her run like with Sisko and his mother journey, Garak suffering from a disorder, having a Silence of the Lambs moment with her older self, Worf and her confliction being Dax and marriage, I thought the crew were too old for her to have some common ground with. I like the idea of Jake being with her and having stories with her, it sure would've made Jake interesting in that season where he wasn't around much. Also, I love seeing interracial relationships and they're no different than any other relationship.