My cave crocodile hatchlings from the last batch aren't all tamed yet! It's been so long that they've reverted from exceptional training to fine training, and that was only one cluster of eggs; I'm expecting multiple clusters now! The fact that Crowgravel has reached the "knowledgeable" training level for cave crocodiles should help, but the real problem is the dwarf I assigned to them doesn't just go out and train them. Apparently, he has better things to do than his bloody designated profession. Maybe I'll disable hauling on him and see if that helps....or maybe I already have over 50 cave crocodiles and I'm worrying about nothing. Still, the same dwarf is assigned to my giant bats and will be assigned to train their offpsring whenever they decide to give birth, and I've noticed my the other guy who I've assigned to my tigers and jabberers has the same problem. Why do animal trainers take so long to tame infants?
Here's how I believe animal training works. I have not looked at the code, but I have trained a lot of batches of cave crocs.
A job to tame a wild animal is generated immediately when you queue the animal for training, and it's a high-priority job so animal trainers do it as soon as they are free from whatever they're up to when you issue the order. Thereafter, animals lose 1 training level per season if they are not attended.
Shortly before this is going to occur, the game generates jobs for all trained animals for someone to come train them again. The animal trainers then move amongst them in random order (depending on which animal is closest to them, just like with other jobs). If the point comes where the animals the trainers haven't gotten to yet lose a training level, the jobs are cancelled and the animal trainers go back to whatever they normally do until the season again ends and the cycle starts over.
It is common for crocs and other animals to hatch shortly before the seasonal training sessions end, so I get 3-5 croc hatchlings trained to tame immediately, but have to wait until the next seasonal training for more to be tamed. If I have a boatload of crocs and only 1 or 2 trainers, it takes many seasons for the trainers to get to them all.
The best way to fix this problem is to have more trainers, and to allow any animal to be trained by any trainer.