In Canada, adult amateurs can show large ponies only in rated hunters,and in classes over fences up to 3’. If an adult is showing the pony, a junior cannot show the same pony at that show.
Hope that helps. If you’re reading the EC rulebook, make sure you’re looking at the Hunter/Jumper/Eq/Hack portion (section G). Here are the actual words from the book - it’s in Section G, Part 2, Chapter 2:
ARTICLE G201 GENERAL
- Entries in hunter classes shall be over 14.2 hands except:
a) in pony hunter divisions restricted to juniors
b) in Adult Amateur classes where fences do not exceed 3’ (0.90 m), Adult Amateurs may ride large ponies. See also: Articles G306.2, G307, and G309.4 regarding cross-entry restrictions for ponies.
- Adults are permitted to show (be judged) on large ponies in miscellaneous non-point classes not limited to juniors. A pony shown in judged classes by an adult may not be shown in judged classes by a junior at the same competition
The Jumpers section does not actually specify anything about adults on ponies. The only reference to ponies is specifically discussing pony jumper divisions, which are open to juniors only. However, the amateur divisions 1.0m and up specifically say “horse” so if you want to show a pony, you should check with EC as the rulebook does generally distinguish between “horse” and “pony” throughout.