There are some interesting documentaries on this. Check out YouTube. The former soviet bloc used to 'talent scout' v young children, take them to boarding school where they would do gymnastics full time. It was seen as an honourable thing to be selected, to represent one's country, and also bring in a better income to your family..but as you can imagine for such young kids it would be difficult.
Not sure how much it happens now, I get the feeing things have cooled off a bit. You might want to read Olga Korbut's biography for an eye opener. V different to what would have been acceptable in the UK.
The female gymnasts in this Olympics are 16-41. The lower age limit is there for a reason - to ensure that they are more able to cope with the challenges of international competition. It's a career, whether they are at the start or end. They take it seriously, but actually, I've seen more smile in this competition than in previous Olympics.
Training hours are long, but similarly because the physical and mental sacrifices are such, the gymnasts wouldnt be there unless they wanted to be. When I stopped absolutely loving it, I stopped competing. It wasn't worth it anymore. Nobody forces these athletes to carry on.
As for the 'screaming in pain' thing, the coaches are doing something wrong if that is the case. There's discomfort (which can be sort of nice) caused by stretching (think yoga) and then there's very real pain / injury caused by over-stretching.
Given the hours that these athletes train, their bodies are, over many years, conditioned to be strong yet flexible. It shouldn't require pain to do that - it should be a long term strategy. Apparently you could wake up these competitors at 3am and ask them to do the splits - they'd be able to do it with no warm up and no discomfort - you don't get that from forcing your body into positions it hasn't been conditioned for.
As for the injuries, count the bandages / supports / tapes holding the gymnasts together!!! They are doing intense physical activity for up to 30 hours a week, so yes, in the long term, ankles get weak, knees get sore, shoulders pop out. This'd be the case in most Olympic level sports though?
In the long term it's a weight bearing activity which is thought to reduce the risk of osteoporosis, whereas something like ballet does not bear so much weight and (I think!) has a much more negative impact on bone density.
I know that I wouldn't have half the back / knee discomfort I have these days if I hadn't been a gymnast, but at the same time I wouldnt hesitate to encourage my child if they were interested and committed enough. Well worth it for the personal attributes e.g. good teamwork, determination to keep going after an injury, accepting that you aren't the best at something, time management, personal organisation.....etc etc...
Sorry for mega reply?!?!