My Mac is 12-1/2 weeks old and he's been lifting his leg since he was 9-1/2 weeks old (honest!). I had posted about it a couple of weeks ago and someone else said their male started early too. It's not everytime as Mac only lifts his leg about 25% of the time - otherwise he squats to pee.
I also have a 2 year old male Shih Tzu that has never lifted his leg to pee.