Description of method:
Letting your child tell you when he/she is ready.
Show them your potty and let them know what it is there for. Don't ask them every 5 minutes if they have to go. This may discourage them. Keep the potty where they kids are, the playroom, family room...
if you see that they have to go, ask them, don't force. It should be up to them. My son "trained himself" in a few days, but only after we stopped forcing the issue.

Recommended age for this method:
It's up to the child.

How long should it take for child to be potty trained by this method?
Once again, it's up to the child.