I bought a 6 year old last fall. Now he's 7, right in nice early adulthood. He's fantastic, easy going, has a good work ethic, and is forgiving of my mistakes. He also relies heavily on me to be a good leader (he's low/middle in the herd) and gets stirred up/reactive when other horses do and can be mildly spooky, though he is improving in both regards. He will challenge people, but only a bit and accepts that they're in charge easily.
When does a horse really mature? I know their training and technical skills can improve essentially forever, but when do you know their personality and attitude have settled? Eventually, I would love for this guy to be a bit more steady/btdt so he can be my babysitter for less experienced riders (friends, family, etc). Is that something that will come with more time, maturity and experience/training, or do you think a 7 year old horse is already set in their way of approaching life and riders?
What's the difference between a 7 year old and a 5 year old? Or a 3 year old? Or a 10 year old?