I did some play testing of the game 'Pigz' with my cousins on the weekend. It's very evident how experience with devices like iPads (touch interfaces) makes a significant difference in confidence levels with an interface whereas their age is less relevant. The youngest child who spends more time on devices than her older counterparts, navigated the interface with confidence - innately hitting the replay and home button with absolute assurance. Her older less experienced cousins were much more cautious.
Age can determine content design but it seems less relevant in determining interface design Interface systems, touch screens have changed the rules. They clearly are less intimidating as any age group seems to 'get it'. Compared to the old days of the frightening icons, cursor, mouse and never ending demands of hand, eye and mind coordination. The use of ones finger to touch is so much more natural than dragging a mouse. Personally I fell in love with the mouse the first time I saw it but I guess I was comparing them to the command line interface - so it is all relative or evolutionary I suggest.