I am in my mid 30's and I am going noticably gray. My temples are salt & pepper,with a little more salt than pepper these days. My beard has lots of gray as well.
I don't care personally, but my wife keeps pushing me to dye my hair to cover up they gray. She is perplexed by my resistance to the idea. I find it unmanly and vain. I also feel like to acknowledge it would be an admission that I am getting old.
Well, this lady's perspective is that grey hair is extremely distinguished and downright sexy. Although I understand your wife's perspective: grey beard hairs in particular can age a fellow, and your wife may not want people to think she's involved in a May/December romance. All I can say is don't dye the hair if you're not willing to dye the beard, which sounds like a bit of a hassle. Maybe trim your beard back a bit, if it isn't already, to minimize the visible grey?
I don't think it's unmanly, and as far as vain, well, if you were in your 70s, I'd say perhaps it is, but you are a young man yet and it's clear that you grey is premature.
I got whitewalls when the walls turned white.
Worked for me.