Originally Posted by Stacymcw
I think horses should be at least 4 years of age before med fence work, then work from 4 -5 over med fence work and work your way up to larger fences throughtout the 5th year.
The OP is not jumping - she is doing distance riding.
I did start my mare at 4. With the rides monitored by vets, they will keep a close watch on your mare. One easy 25 a month should be ok.