Firstly, Good Luck with your stage 3!
I am also turning 32 this year, so have the same concerns as you. Albeit Stage 1 & Stage 2 are a more pressing concern.
I keep telling myself, that surely they wouldn't let you get through to the later stages of the process if they were only going to bin you, due to your age at the final hurdle. Would be a massive waste of resources and effort on their behalf surely? (fingers crossed)
Best of luck once again, just go in there and do your best and try not to let your doubts about your age affect you. (easier said than done I now)