While reining is tough physically on the horse, I don’t know that I would go so far as to compare it to racing. I really believe that training practices and management in the barn can go a long way to extending the career of a reiner (things like a slight change in hoof angle can make a big difference on the joints of a reiner). While a majority of the horses showing WEG reining were 6-8 years old a good number were 9 or older. By my count of the entries, out of 63 horses that showed in the team competition there was one 14 year old, one 13 year old, four 12 year olds, two 11 year olds, five 10 year olds, and eight 9 year olds. While these horses are still probably quite a bit younger than the dressage horses or jumpers I am encouraged that there are more than one or two reiners out there proving that older horses can continue to show at this level.
Many of these horses start their competition careers in the fall of their 3 year old year. There is a lot of money to be won in the 3,4,5, and 6 year old classes (note a couple of the horses showing have $300k- $400k+ in earnings). In the last month or so one of the biggest money reining shows in the US, the National Reining Breeders Classic, announced the addition of a 7yo and older class to promote the FEI level horses. I personally think that this along with the growth of reining as an FEI sport will encourage owners and riders to keep the horses in the show pen longer.