i always start them with an experienced dog, give them plenty doubled up to start and keep them winning, but i expect them to be single handed by 2 y/o...
you can tell usually when the dog is ready for one on it's own, but some never even get that far, you can perservere for ever but if it's not there it's not going to happen, and this is the case with 90% of dogs imo....
doubleing up for to long leads them to rely on the other dog, and i've seen loads that look the part, and even act the part when in the company of another dog, but put them out on there own and there shite....
try the dog