"Anonymouse I think you have missed the point by not understanding your own writting. You wrote provided you get yourself to a good teacher. Where are the good teachers. If they are not where you live and the competitions are also not where you live what do you do. Read the original thread."
In a word, you move where they are.
Without taking that chance, and trying things with the kind of teacher who has a history of creating champions, there is no way to improve on the kind of go/no-go deteremination that a non-expert could make: do you have the time? the general physical fitness? the deteremination? Simple questions like that are all that can be asked until the experiment is tried.
"He said i didn't have the heart to tell them that in his opinion they just weren't good enough."
In that case he is eaither incompetent as a teacher, or he mis-spoke and what he really meant to say is "they are not committed enough".
The point of a teacher is not to tell someone how to do what they are a supposed "natural" at, it is to teach them how to do what they DO NOT know how to.
"They gave up dancing completely after turning profession for a spell."
Then they didn't have the "need" to succede, without which high level achievement is impossible. If you can walk away, then it's not for you.
"She had a weight problem and was turning into a barrel."
Physical fitness is a requirement, any bloke off the street can tell you that. It can also be addressed in most cases.