Big 2 yr old races??

First off humans do not stop developing when they are 18. Men really do not stop developing until they are 25 or 27. Women tend to stop developing much earier. I think it is like 19-21.

Horses physically develop much faster than humans. As for as life span is concerned 1 year for a horse is equal to about 4 human years. So a 20 year old horse is an 80 year old person. But it would be hard to measure and compare a horses physical maturity vs a humans. Humans develop over the course of 25 years. Horses develop in a span of 7 years.

But I see no harm in racing horses at a young age. If he we (human) didnt inject drugs and special feed to these horses at a young age then maybe they wouldnt break down so much. If we let them develop naturally then maybe these horses would be sound for a longer period of time.