Which PvP are you referring to? Arena or Tower?
In the Arena, if you choose the hardest opponent, you can fight up to 3 ages above your age. So, VF is well within the bounds for FE.
In the Tower, it could be there were not enough members in your age to fill your neighborhood, so they can use higher age members, usually just 1 age above. However, if a neighbor power ages several ages up and garners their current age troops, they could put them in city defense, so yeah you would be fighting VF troops with FE troops.
There are also ways to accumulate higher age troops, but I have never seen VF troops for FE age members. It may be able to be done, but I am unaware of it.