Age gap

I’m a 25 year old female, and have been seeing a man who is 11 years older than me for almost 2 years now- recently one of his female friends brought up to him our age gap and made comments about him being immature and “weird” for going for a younger woman like the stereotypical creepy older man jokes. This kind of thing usually doesn’t bother him but it seems he’s kinda stuck on her comments, he’s mentioned it a few times and now is a lot more aware of everyone else opinions and almost feels like everyone’s judging him. I’m not really sure on how to comfort him as I would typically just make a joke about things but I feel he’s a bit sensitive to that atm. so any advice on how I should approach it will be ace. Thanks