One, 29 is not old!! You're as old as you feel, remember that!!
I've only been in HK for 3 months and have yet to scratch the surface on the nightlife. Granted there is basically three areas that I'm familiar with: LKF, Wan Chai, and Soho. Some of the better clubs I've been to, Dragon I and Key Club in LKF, I think you have to be a member of....not totally sure, but I would check out Dragon I if you can, it's been my favorite so far. There's also a couple places in Wan Chai called 1/5 and Mesime<--spelled wrong, I'm sure-- that plays good music. Or, if you go out during the week, Swindlers in Wan Chai is very small but has a great band on Wednesday nights.
You'll eventually find something you like. Try picking up one of those HK papers that comes out weekly to see what's happening for the upcoming weekend, that should at least get you started.
Good luck and stop acting like a Grandpa, 29 is not old!