If your horse enjoys it, and he is relatively good shape, I see no problem with it.
There was a thread similar to this one started a day or 2 ago. I will give you the same advice I gave to the OP of that thread:
A training tip for you:
Slow work can be just as (if not more) effective as fast paced work. Running perfect patterns at the walk/trot will translate to better runs when you put the speed into the mix. It is also better on the horse.
Read more: Is she to old ?
If you want to read through that thread, this is the link to it ^.
EDIT*: I will warn you that some of the posts are somewhat blunt.