My now 3 year old was taught good ground manners because they didnt exist, which involved standing tied, grooming, feet picked up/trimmed, lead well and move away from pressure, rugging, booting, washing ect as well as respecting person space (the really hard bit that he still struggles with at times
) and all that was done when I got him as a yearling which in theory he should have been taught as a foal.
As a 2 year old I taught him to lunge and long line at walk to let him get a feel for it (no longer than 5 mins) after getting him use to a bridle and roller and finding a bit he liked
Lots of inhand work in traffic, off and the yard, let him see a ground pole, tarp and generally desensitize him to scary things and teaching him how to react in a respectable manner if he does find something he is unsure of ie no bucking, bolting, rearing or sitting on mummies shoulders
.
Now as a 3 year old and having the winter to himself doing nothing but eat and poop he has had me lean over him (9.5-10stone...hardly much weight for his size
) and he is to start proper long lining with a gentle lunging session to get him to build his muscle up...lots more walks out in tack with/without company, starting to have weight on his back more and walk around with a rider. Depending on how it all goes and if he takes to it well he might start to go on small hacks until having another winter in the field, if is finding it all a bit much I will just stick him back in the field and try again winter
My other youngster (rising 3) still cant pick her feet up properly so we have a long way to go with her and she might not even start the groundwork until a 4 year old, so its not important to have done it as a 2 year old...but the ground/foundation work has to be there before you try and get on board or you will end up getting hurt or have a really 'naughty' horse that really just doesn't understand.