In my opinion there is nothing wrong with riding an older Bike. You just have to make sure it is safe. Old bikes depending on how abused they are might have weld cracks or stress fractures. Karpiels, Intense used to have issues at the welds and Santa Cruz Super 8's broke the rear swing arm at the dropout. I have a 1998 Foes DHS Slammer tube with a 2001 Monster-T 3" Gazzi conversion. Fork has 6.5" rear a solid 8" travel. It was my old race rig and one of the fastest on the east coast back in 2001.
I went to rebuild it this year after taking a 12 year leave of the DH scene due to injury and noticed 3 weld cracks after i removed the paint. One along the bottom gusset of the head tube and two at the upper welds of the bottom bracket housing. If it can be rewelded professionally I will rebuild it. But I don't think I will be dropping 10+ foot drops on it. I'll just use it for flowwy stuff. If it can't be fixed it will be great wall art.
Im actually in the process of building up a ten year old brodie nemesis with parts i have had lying around the house. Will make a good trail beater bike
This is currently in my loft in pieces, every year I say 'this is the year' and I kid myself I'm gonna rebuild it. The matt paintjob was mostly stripped with Nitromors several years go, just the webs in the arches have some old paint in. The bearings are toast as well. I took a while out then had a crap weekend racing it back in '09, put it away and not sat on it since, so aside for the want of new bearings and cleaning it up (still some Dunkeld mud on it) there is nothing wrong with it.
Only upgrades since new were replacing the fugly double drop post and upgrading the E4/Mini to Mono M4's. I also bought another pair of '04 Super T's, upgraded one leg with HSCV and sold the second pair with 2x HSV carts as Juniors (which they technically were by that point). Might have broke the mech and a few hangers as well...