Hi Scout! Neither of us have ever put a young up but it is interesting question in that we’ve certainly heard of that practice. I think it mostly occurs with trainers who put too much control or pressure too soon for dogs that aren’t ready or put their dogs in situations over their heads, diminishing their dogs keenness.
We go the other way, getting he dogs to enjoy it as much as possible and increasing enthusiasm (too keen is more of a problem for us !) to your point, we may work a keen young dog 3 times a day in a shorter 5 min sessions versus a single 15 min session.
When we’ve had dogs that we’d like to see become more keen, sometimes we change the working pattern for a week or 2. For example, we will work them for 3 days in row and then give them a break for 3 days in a row. This often makes the desire for getting back on sheep build up and the anticipation becomes the boost they need. We generally start our dog between 8-11 months old. I hope I answered what you were asking. If not, please let me know, cheers,