I have an APHA filly who was born in late August 2011. I have worked with her since she was about 8 months old, and she is a very mature and easy-going horse.
Since she was born pretty late and was behind her half-siblings (all 8 mares were bred to the same stallion) in growth, starting her this spring and late summer was out of the question.
Though in show years she is 3, she is now 2 years and 4 months old. She is about 14.2 hh, and will probably mature to about 15.2 or so.
When do you know a horse is okay to start under saddle? When would you think, without knowing the filly or seeing her, she is okay to start?