We have a bunch of heifers here for the summer. The owners bring them out and leave them until fall. They have a bunch, and I mean a bunch, of yearling bulls running with them. This late summer, the heifers will all be ultra sounded for pregnancy confirmation and the date. They will be marked as to their calving date, sorted into groups and then offered for sale.
The owners also raise bulls and so they buy back heifer calves from the people who buy their bulls and most of these are from that. There are also some they raised on their own ranch.
They were mostly wintered in a lot and are very gentle and friendly. Almost too friendly!
When you ride out and around them or thru them, they will come up to meet you. I can imagine their conversation.
“Hey dude, whatcha doin’? Did you bring us some feed? How about some of that good ground corn? Or some salt? Man! I love salt! NO! I really mean it! I really, really, really, really love salt!!!! Dude, why didn’t you bring us some?”
Yeah. Just like a bunch of friendly teenagers. And they are are almost impossible to drive as a group. They take off in a mad stampede and then stop and look around to see why they were running. And just like teenage boys, there are always a bunch of bulls who have a heifer singled out and trying to convince her they are the best thing in the world!
The poor little heifer is bewildered and wants no part of them, but eventually she just gets worn out and has to put up with their awkward advances!
If I had a couple older cows or a good lead steer with them it would help. They act like a counselor on a high school trip. They know where the gates are and if it is a big horned steer or even a horned cow, they don’t put up with any foolishness. Any youngster who gets out of line is put in their place forthwith!
Most people don’t like running yearlings. I do. For one thing, when you move them you don’t have to pair them up after the move. They have never established their eating patterns so will eat about anything put in front of them (Imagine hungry teenagers) so the forage gets mowed down more evenly. And when (there has never, ever so far, been a if, in this matter) when one gets a bad foot or a bad eye, they are not as big and are easier to handle when you rope and doctor them.
We (my son, his two sons and a guest) rode up the other afternoon and roped and doctored 5 bulls. (Yeah, that was about 10 percent of the bulls, they have been working hard!) The older son was riding a horse who is not finished in his training as was his younger brother. So the youngsters got the first go at catching the foot rots. It is a great way to train a horse and gives the kids some great training while under the watchful eye of older and hopefully wiser hands. And sure nice for old fat guys when you got a kid to get off and administer the shot and take the head rope off!
It went well, but we all were sweating when it was done. Except the guest and his horse, who just rode along and watched the show. Seems they do it different where he came from!
Anyway, summer has been interesting and here in another week when I turn my little bunch of cows and calves with them, I am sure the pasture moves will get easier. I haven’t turned them out sooner as I really don’t want cows calving in March of next year!
Don’t let your horse fall down on you and get your head under you!
Dennisranch 
Your description of comparing the yearlings to teenagers is right on. All energy, hormones and no brains.