As an old fogey myself (43, with premature grey hair), I go to hard rock concerts all the time (Audioslave, Coldplay, Disturbed, Godsmack, STP, etc...) and have never gotten bothered by anyone.
Two bits of advice:
One, staying out of the Mosh pit area is good advice from Riley804.
(FYI: The Mosh pit is the area directly in front of the stage where the kids (Man, I feel old for saying that!), lift their buddies up and push them around over their heads, until they reach the edge of the pit, at which point they usually fall to the ground, sometimes on people, and usually on their heads!)
Two, bring some small, in the ear earplugs (or wads of tissue). If you sit near the speakers (and near means within 50 yards!), your ears can get temporary or even permanent damage relatively quickly. Putting in the ear plugs will only slightly dampen the sound, but will protect your delicate eardrums from being damaged, thus ruining the years of effort of putting together a multi-thousand dollar stereo system. (STP had my ear ringing for a couple of months before it cleared up. Thank God!)
PS Both Audioslave and Coldplay are currently touring, and both are putting on great shows!
Have fun! I wish I could go, but it is during the week in my location, and we don't have daycare for the young one, and two years old is way to young for that kind of music!
