I probably passed my refs exam at a similar age,early to mid thirties,but I'd suggest you have a good few years if you want to advance. I'm now too old for any lists at all.Absolutely this. I'm impressed with the time and commitment that some posters put in to their refereeing.
I got in to it too late (37 years old) to make any real progress up the ranks but I still find the younger, more ambitious referees attitudes quite inspiring.
The process of progression looks quite attritional at times with little financial reward (as evidenced by the low fees highlighted on this thread) and lots of hard work which I suppose is a decent barometer for who really wants it most.