Q:

When did Cardassia first achieve interstellar travel?

I know that it is established in DS9 that Bajorans used their solar sailors to travel as far as Cardassia before the Cardassians had achieved interstellar travel, but when did the Cardassians actually achieve interstellar travel and become warp-capable? Any answers canon or not would be appreciated, as long as the answer is derived from a published Star Trek work. 

A:

Neither memory Alpha nor Memory Beta provide an actual year for when the Cardassians first became warp-capable, but a line spoken in ENT: "Observer Effect" puts it at no later than 2154. 
A pair of Organian scientists are observing the Enterprise crew react to a deadly virus found on the planet below, and one says:

Oh, I don't know. They're showing concern for each other. The Cardassians did that when they were here, didn't they?

(emphasis mine) (taken from the script). 
This assumes that the Cardassians traveled to this planet under their own power. the Organians would not have brought them there as they had a strict non-interference policy regarding their observations, but this doesn't rule out the Q or some other bizarre phenomenon being responsible for their displacement. 

A:

The reference book "Star Trek : Star Charts" lists Cardassia Prime as having become warp capable in 1925 AD. First contact between Cardassia and another planet (Bajor) appears to have happened much earlier, in 1571 AD.

