No, I think it's only in this one word. We never write rageing or pageing; they're mistakes pure and simple. I don't know why ageing should have its E.

How odd, I've just checked Modern English Usage. Fowler discusses rules and exceptions under Mute E, and gives lists of examples, but nowhere mentions 'age'. So the rules make it 'aging', and his lack of mention of 'ageing' suggest to me it's a recent innovation. Anyway, it is now the almost universal British spelling.