Just in the last few weeks my normally placid 8 month puppy has started to get hyper when we (especially my teenage daughter) goes upstairs he usually rushes up before us and then barks and try to mouth/bite getting very excited.
We have tried firmly saying leave/gently pushing him away/calmly talking to him as we approach. Not much is working, when we go into our bedroom and close the door on him, it is like the hound of the baskervilles!!
After a minute or so when we come out, he is just fine.
Any advice please would be most welcome.

Most teenagers I know 'stomp' upstairs - perhaps this is setting him off?  Could you ask her to walk calmly upstairs and see if this makes a difference?

why not put a gate on and stop him going up stairs.

My 6 year old sometimes still does this especially to my son, it is a King of the Castle type game.

Don't allow her uyp the stairs at all or only on lead where you can control the situation, and stay calm.  It shoudl be discouraged as it could cause someone to fall and hurt themselves or the dog.