Don't be intimidated by people who are older than you, have more credentials than you or have the 'gift of the gab'. Just be yourself, relax, treat it as experience if nothing else, give it your best shot and don't be shy!
Everyone is the in the same boat, it all depends on how you perform on the day and how you come across. If you have met the minimum requirements in order for you to attend the selection, then you have as good a chance of being successful as the next guy!
Good luck!