I need to go from Kingsbury Station, NW9 to Chalfont & Latimer Rail Station on Sunday. I am 16 and have a 16+ photo oyster card (free travel on bus), i was wondering if i can top up money on there or not? Also does the oyster allow me to travel on the Chiltern Railways?? Or do i have buy another travel card?

You can only use PAYG on for the stations show in green on this map

http://www.tfl.gov.uk/assets/downloads/tickets/oyster-PAYG-08-01-02.pdf

However Kingsbury is on the Jubilee Line and Chalfont on the Met Line. So the easiest way is to change between the 2 at Wembly Park.

You can put PAYG money on your 16+ Oyster, my daughter does.