I've had no singing experience and I've been putting this off for a long time but I want to learn how to sing, in the vein of 80's metal vocals. Is 30 too old to pick it up?
physically? i have no idea.
mentally? FUCK NO! you can do anything you set your mind to man. youtube has some tutorials on exercises im sure. plenty of tips to get you started.
not an 80's metal band, but my advice to anyone who wants to sing is to get a copy of "In an Aeroplane Over the Sea" by neutral milk hotel, learn every word, and sing along as loud as you can. the guy has no concept of vocal range, and it really helped me in expanding beyond my comfort zone vocally. the music is... an acquired taste, for sure. but i think as an exercise it works.
When I was 16 I was worried that I was too old to start learning guitar. As a 30 year old I'm sure you can appreciate how silly that sounds. A 50 year old would probably think that you sound pretty silly right now.

I could say the cliche "you're never too old to learn", but maybe a better phrase is "never deny yourself something you want".
And no, Guitar Hero will not help. Even on expert. Really.