Wait what? That seems insanely long. When you say average wage are you talking across all disciplines or whatever your industry may be? You might already know about unbury.us but it's a very useful tool for student loan repayment estimation.
I used the calculator at MoneySavingExpert, I have one loan on the old system at ~£22,000, assuming I earn £25,000 (which I do not expect to earn at all, but hey it would be nice) it estimates it will take 16 years and 6 months. My new loan to cover this year of teacher training is ~£17,000, but because of the different rules for the new system it estimates repayment in 16 years and 4 months. I have no idea if it tries to pay them both off at the same time or not, in the UK it's automatically deducted from income so I will have to start earning and find out! I hope it doesn't though, as that would be two 9%'s coming off of my paycheck.