It has become very common to hear the "not till 12 months" or "not till the growth plates close" or not till <your choice>.
What some "experts"/trainers/top handlers say in public isn't necessarily what they do in private. I've been surprised more than just a few times as to the differences, and by whom.
There are differences in opinion & approach - there are trainers jumping their dogs before 6 months of age and up. There are handlers who can start their young pup at 15 months & stride through novice to Masters with few if any NQ's. There are some who have taken their pups & won Regionals Tournaments before doing Starters. There are some who regularly train at international level before their pups are 2 years old.
Not saying any of this is right or wrong, just that it does happen & there are different opinions - and so it is plausible that some students are doing things earlier than what others consider to young.
In some ways I think it is sad to be pushing pups too young knowing or disbelieving what others might offer as advice.
Most of the experienced handlers that I know won't start training their dogs until at least 6 months old in any agility at all. I know of one very good handler(competes in Nationals, teaches classes, etc.) that got a new puppy not too long ago and refuses to train agility with him until he's a year old. She thinks he needs time to be a puppy without the added pressure of agility expectations.
I don't think I can wait that long though with my new puppy. I'll be doing tunnels and jumps with the bars on the ground soon as a fun activity, but I'll wait on weaves and contact equipment until he's older.
but he loves to play the games.
Even if he is ready for it, there won't be much point if I've not come up to scratch!!