If you are talking about a historical or archaeological 'age', then there are several options. Oes is quite common. Have a look under 'age' here for some examples.
ers achau is a common idiom but, like many idioms, a word-for-word translation is not very helpful - achau these days is usually used to refer to your family tree and ancestors.
So it's really more like "I've been here for generations" (even though that isn't the standard phrase in English, I guess)? I know that it was possible to use the equivalent of that phrase in Swedish in the past, though nowadays everything taking longer than 5 minutes is taking an eternity... :-)