Hell, at my age a kid on a 125 could eat me & the XR up on a single track, that's why I tend to stick to fire roads and 2-tracks. Have outrun a number of modern bikes, including even a 2010 Husky 540...but I attribute that to 45+yrs experience versus his 4-5yrs. My racing started with scrambles in the mid-60's, some short track, few enduros and CC races thrown in, too. Back then in D-14, on any given weekend, within a 100mi radius, you could pic most any kind of racing you wanted to, often having choices to 3-4 scrambles on any given Sunday. You should have seen the look on the boys face when my wife told them about my running short track with no brakes.
Buckeye....you need to find a real vintage bike.....a pre-74 twin shocker. That'll give you a work-out.
Got an '85 XR350r that is sitting around waiting for a new piston to turn up somwhere....only ran that piston for 1 year, so hard to find.
If you find yourself an '82-83 CR125, let me know, I got a couple of good old motors for them.