Hi, yes we did the qualifiers last year. They are held after the BIS. There is no age limit as such, but the rule is, that the dog must have qualified for it's JW between 'X' date & 'X' date, which I think is the end of August. So it could have got it's final point on the 1st september, turned 18 months on the 2nd, and then be nearly 2 1/2 by the time it comes to the qualifying. My lad was only 10 months when he qualified for the semi finals, and against some much older dogs.
I think it is the BIS judge that does the selecting, at least it was in the two qualifiers I went in for. To get a list of shows which are holding them, ring the KC, they'll send you a list.