DeletedUser25273
My understanding is medal expansions are not limited by age, only diamond expansion are (There are exactly 2 diamond expansions available per age, and about, but not exactly, the same number of victory expansions). They seem to add a couple each time they open a new era, but there isn't a requirement to be that new era to get them. The expansions earn from the tech tree are of course limited by age, and the expansions from the campaign map limited by your advancement on the map, which is only roughly limited by age.