this may sound sooo stupid but i got some leaflets from a local tack shops as you do, for some competetions one of them was a 'senior one day event'. does senior mean you have to be over a certain age...?
Senior to me would be over 14.2hh... like with BSJA. Doesn't mean you have to be a certain age. Although, with Juniors and BSJA you have to be under 16, so may be you have to be over 16!?!?!
I may be wrong.....but Senior normally means that you were 17 years or over before 1st january of the season you are competing in. Basically id you were 17 years old or more last year then you will a senior for this season.
For pony club senior one day events, it just means that is of a bit of a higher level i.e bigger jumps and more complicated dressage tests. If the class stipulates no age then there is no age restriction.