(I just realized I hadn't yet responded with my perspective on the thread topic.)
I have no reason, or knowledge, with which to argue with current scientific estimations of around 14 billion years old. My personal guess would be to use a term like a bazillion.
As have been mentioned by some others, I don't see that it matters much in my daily life how old it is. The only time I even think or talk about it is here on RF.
Generally, I think just about everything goes through cycles of organization, growth, and death -- so I expect the earth and the universe may do that as well, at some point, eventually -- but I don't think I'll be here in this body when it happens.