I don't have data to back it up but I feel advanced user have less chances to getting the answer right away. The reason being they need people with more knowledge and experience to solve a problem.
Now the motivational system on SO for someone to answer a question is points. Therefore an advanced user is more likely to get an answer if the question has a bounty attached to it.
The point I am trying to make is that there should be a way to calculate, based on previous user data, how long he has to wait before he can start a bounty? The present system of evenly waiting for two days for everyone needs an overhaul?