Grow a lady Moustache :D No don't do that really. I grow mine because I look like a kid without it. But if you're intimidated by it, I'll probably keep it shorter, you know incase other girls think that. :)
I'm on and off about mine sometimes I grow it slightly because I look very young other wise but after a while I shave it off, I feel like I look cleaner that way. Ladies can look more mature in the way they dress. Dress more intelligently and more sophisticated.
When I was 18, I dated someone who was 21 and despite that only being three years, when he'd grow out his stubble, we'd look a lot more obscure, I used to purposely ask him to have a shave every time we'd go out in the day haha, commitment! I think for me, maturity within women depends a lot on the clothes you wear, I'm only young so obviously I'm showing my legs off and all over the place but have you noticed when women become older they sort of seem to tone down the fashion? Become a little more reserved, blend in more, that's my take on it anyway but by no means should you even think about doing that. Don't let it get to you, they are only strangers, you're never going to see them again whenever you see them out so who cares? As long as you're both happy, this should really be the least of your worries. If it really bothers you that much, his next birthday or whatever buy him a really good electric shaver and be subtle, you'll work it out.