I just started @ 50 too and I'm having a blast!! Should have started racing after divorcing first wife! Anyway I feel ya on an old kart. I stumbled on what is probably a twister non adjustable front end but I found a track it loves. 1/5 mile right beside a creek little wet sometimes and it excels. Price of karts mine was 400$ it's probably 20-25 yrs old. Double that to 800 or 1000 and get a newer easier to get parts and setup numbers. But for now I'm happy as can be with mine!
I'll second Panther X. If you want to restore it, they're a very sought after vintage chassis, especially if it still has the original Margay three piece wheels. It's too old to be competitive with modern stuff though.