Hi Vallada,

Here's been my experience. While it may be true that some horses will not improve (although I've seen some very small improvement to some stats through the training process), some do tend to hold on to heir peak performance longer than others. In addition, I find that sprint horses will mature faster than distance horses. Some of my longer distance horses have shown the biggest transformation at the end of their 3's or at the beginning of their 4's.

I don't know if this is a quirk but I have one sire that consistently produces late bloomers. One horse in particular has won 5 out of 6 G1 races (one 2nd on an unfavorable track) at 4yo and 4 out of 4 G1 races at 5yo. I even tried her at 6yo once in a G1 before I retired her and she ran 2nd beaten a nose. But as you can tell, I'm not so quick to cull or retire my horses for breeding without giving them a chance to prove they have something.