I don't make shit up. It's in the movie. I'll go directly to the script.
...And, as we found, it's not.
Like
JonnyQuest037 says, there's Goldilocks' portion of ambiguity there, from that prominent separation between the "century" bit and the "warp and thugs" bit.
But that's selling it short, really. Conceptually, indeed semantically, it really means what it should - what Picard has to say about dealing with the Romulans is in response to what Dougherty has to say about dealing with the thugs that are the Son'a, which means that the folks in question
already have what makes them more than thugs. That is, the Son'a have it now, so the Romulans had it then.
Even if the writers intended to say that Romulans only got warp a century ago, they didn't say it. (Although I doubt they ever did intend such a thing.) What they did end up saying was right on the mark: dealing with nasty pieces of work just because they have peer qualities (oil, warp, fountain-of-youth-pumping tech) is not gonna make your dad proud.
Although it's not a perfect analogy. Controlling oil today is a knife on your throat. Having tech that can recover the secret of youth where yours can't is a knife on your throat. But having warp merely gives the Romulans a fighting chance; it's not a knife on your throat. Invisibility tech might have been a better choice there. And, incidentally, something the heroes feel is a century old at this point...
...Which is the bit of canon
I would like to erase. It's profoundly silly that our heroes would first encounter invisibility as late in the game as "Balance of Terror". They take it, and so many other things, in the stride in all other adventures, before and after "BoT" (in both airdate and in-universe terms); they shouldn't have declared it "theoretical" in this one. Especially when the story was about fighting a submarine with ASW weapons, which Kirk can't have if his side doesn't believe that submarines exist!
Timo Saloniemi