I'm assuming that you're asking about the TCG? If that's the case, then any sets after Black & White Next Destinies aren't able to be used in official league play under the Modified Format. You can still collect the older cards and play with them recreationally, though.
Since I'm not an expert on the card game though, I'll move your thread over to our Pokemon TCG forum, in case you have any more questions or you'd like someone to elaborate a bit further.
For play amongst friends, you can use cards from any set, as long as it's an actual card from the Pokemon Trading Card Game, since they are all part of the same game. It's not like they completely changed the rules with the release of each set, just some tweaks every once in a while based on what is becoming problematic at official tournaments.
For official tournament play, the sets you can use are much more restricted. As of right now, the sets listed in the first post of this thread are the only sets that can be used at official tournaments.
This help at all?
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