'Rising' is a term used [in the northern hemisphere] from the 1st january to the horses actual birthday.
This means that if a horse is born 3rd may [like my Rowan] from 1st january 2010 to 3rd may, he is 'Rising 6'
Then, from 3rd may to 1st january 2011, he is just '6'
This is because all horses in the northern part of the world age on the 1st january. This has come from racing, however it actually counts for all horses, Thoroughbred or not. This is that so all horses can be classed by one age.
If you do not know your horses actual birthday, then your horse is effectively a year older on the 1st january.
Horses stop growing around 5-6 however some mature late. Some geldings have been known to still grow upto 8 years old.
Just a few more months and we will be fine RIP Rocky x 92 - 27/06/06 x Your hoofbeats have become the very rhythm of my heart