Gosh! My Daisy, an almost 9 month old yorkie does that too, to this day! but its mostly with strangers and pretty rarely me. We always try to tell guests to ''ignore'' her (I know, it sounds mean) and she usually doesnt pee then. I mean, they usually find it so hard to ignore her because, number 1, she's so cute and number 2, she wont stop ''jumping'' up and down..lol..everyone thinks her legs are gonna snap or something! She def a determined lil one!
The vet thinks she'll grow out of it as she gets older but ''excited pee'' is something that really cant be enforced.