re: How old is Gollum supposed to be?

quote:

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and what marked events was he alive during?

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Sauron became more active in Dol Guldor around the same time Gollum found the ring. The White Council was formed with Saruman as it's leader. Galadriel and Gandalf were also a part of it.

LINK
Just do a search for Smeagol on that page