Looking like a "hot 30 year old gal" is usually a good thing, but I understand, given that you are maybe a full eight years younger than 30, being a 30-anything is not the look you're going for. Aging is a funny thing, and by funny I mean awful. The Barbie bombshell in high school pops up on Facebook looking like her own mother and that Leo look-alike in college now looks like Robert Redford.
I don't know if you and your man look like Demi and Ashton walking through town; I'm not even sure if it has ever crossed his mind or anyone else's that sees you guys. As you probably know, our personal mirrors are more like microscopes illuminating every wrinkle, droop and blemish others might not notice.
In purely cosmetic terms there are lotions and things you can try to help give your skin that rejuvenated look. They are expensive and I'm no expert on which one is right for you. Staying out of the sun and hydrating also help the skin maintain its tone and tightness. Of course for the downright petrified, there's Botox, but I'm not advising you to shoot botulism into your 20-something face - just putting it out there as a "thing" people do.
More importantly, remember this: aging, like other pains in the ass, is the price we pay for continuing to live. We can take steps to preserve our look and live healthy lives, but don't consume yourself with fighting Father Time. He will kick your ass. Also, while your man looks all Haley Joel Osment now, look at Haley Joel Osment now! In other words, he too will start to age when his DNA tells him to.
Who knows, in six years things can even out, or he'll surpass you on the road from ripe to rotting!
Well, if he's with you, I would have to say, if what you are saying is true, then he has clearly looked past your "flaws", real or perceived. Funny guy is correct, we are our own harshest critics, judges who know no mercy. I understand your concerns; no one wants to look like a hot "30 year old" unless they are in fact at least 30 years old, or even better, 40+ years old. Has anyone told you that you look 30? If no one's commenting you look late 20s/early 30s these could be self perceived observations.
Funny Guy tossed out some good ideas. Other things you can do is eat a varied diet, including more antioxidants, get plenty of sleep. Another thing, where women have an advantage, is you can use makeup to conceal any "aging" signs. But before you make any major changes, ask your close friends (not your BF, he probably won't answer objectively) for a straight up no BS answer how old you look. If they're telling you 30ish, then consider the ideas Funny Guy said.
Part of being a younger looking older guy is that you can use your older guy smarts, game and confidence to get younger hotter girls than you could when you were younger.