Look, now - this darling black lab pup came to the house last week. If I hadn't two hellions already, I'd never have given it over to the shelter. About 3 months, I suppose, maybe a bit older...learned the kennel in an hour, had a natural Heel instinct, and played instantly well with my two very rough playing dogs.
He learned to sit, wait, in, out, and even fetched toys to his kennel by himself, selecting a chew toy on his own rather than something naughty.
If you need a VERY smart lab that will be rather large (pontoon paws), please please let me know. We called him Thor...and he'll be an amazing dog for anyone who saves his black hind end.