In NSW there is usually about 4-6, (sometimes more) vets/masters racing 4X most state races. I (age 39) used to do most races up until last year or so but racing less now the second bub arrived.
Hope to get back into it as the kids grow up a bit as it was great fun, especially the usual old guy's sledging the 'young fella's' (ie 30-35yo's) and trying to teach young dogs new tricks (but usually getting spanked).
Be warned though, there's some damn fast old guys lurking around (just not me...)