I don't think it sounds too much for a child to bear. On the contrary, I wish this name would get some circulation in the States. It sounds like a little English chappie, IMO. :) For an older male, it sounds very gentlemanly, like the sort of extinct, chivalrous gentleman who still opens car doors for ladies and stands when a lady leaves and comes back to the dining table. *sigh*
I recommend using
Rupert for a little boy, wholeheartedly.