I'm not looking for intangibles like personality change, etc. That doesn't help solve the ACTUAL problem.
Most Helpful Girl
I'm attracted to older guys, but even I cannot resist a guy who is dressed well.
So my suggestion is just to dress well, especially if you look "hopelessly" young. I would go for a blazer and some nice fitting pants. Baggy pants are really not in anymore. You can even get a leather jacket and pair with your regular t-shirts. Zara has a lot of clothes that really define a clean cut guy who will look not so "hopelessly" young.