At your ages, it would bother me. I feel like 20 and 30 are very different times in your life and what you want in your near futures may not be compatible. It's not the same as 40 and 50 dating. Not saying that it can't work or that you guys don't have the same goals but just that I think it's usually less likely. What I wanted at 20 is not at all similar to what 30 me will want.
I think it would depend on how different the places you guys are in life. I have a kid and I'm 24 so my life is pretty similar to that of someone in their 30s bc I'm pretty settled now. So I'd prefer someone older. But when I was 21 I would've had a hard time with someone 31 bc I was wild and partying and in college with no responsibilities. Hope that helps!