The sign at our local park used to say 12 weeks, but it now says 6 months. Like anyone ever reads the rules! West Park requires them to have a rabies tag to be in the park, DI park also but there has never been anyone there to check! For the pup's safety, he should have all his puppy shots and rabies first. (of course we can smuggle him in for some basenji bonding, Cairo came in as soon as Betsey got him!)
I started at about 4 months. Our dog parks have a small dog area so we started in there. He immediately loved it and it was great to see him push boundaries and then learn from the other dogs, as opposed to me just saying NO. I also made a point to have him meet as many different people as possible–old, young, black, white, wheelchair... everything. Lots of car rides, shopping trips.
He's grown up to be one of the friendliest basenjis I ever met - with both dogs and people. People are usually surprised that he's not cranky or aloof.
Sophie is one who definately thinks that the standard reads "a goof with strangers". She loves meeting and greeting people and dogs though she has learned how to be dog appropriate and is not a push over. She wags her tail so much it is no wonder is is only a loose single curl, how could it be anything else with it in constant motion. We do a lot to socialize all of our pups so they are outgoing and confident but there is a definate distinction between some of our pups who would probably be considered "Aloof" though they are friendly and like attention from strangers, they always make you feel like you are attending court for royalty and Sophie whose dream job would probably be a greeter for WalMart.