My thought has always been that their natural lifespan is around 400 years. I'm not sure if that 100% works out lore-wise, but that's just what I've had in my head all this time. However, I do figure that with technological help the natural lifespan could probably be extended quite a bit.
I don't think it's remotely within our grasp anytime in the foreseeable future, but I don't see why there can't be a "cure" for aging. Most of those processes have to do with DNA shifts and parts wearing out and whatnot. If we had the ability to keep accidental DNA mutations from happening, and a variety of other things at the nano-scale, it seems feasible to live forever. Though something would have to be done about memories in the brain, because eventually those neural pathways are going to be full up. We're already shedding and replacing all our cells anyway, so we just need to do a better job of making sure that the new cells aren't inferior to the ones that came before them.
It is hilariously outside the realm of any current technology, of course. And even for the races in this solar system, it's way outside of the bounds of anything that we've seen them do. But exactly how old this Hydral is at the start of the game is unclear (though it's probably at least 150ish), so he has a pretty good length of time left to him. Even just with some less-drastic health measures, he could live beyond 400, I'd say, and by then who knows? Maybe he's still out there 2000 years later, tooling around the galaxy all by himself. What happens to him after a successful campaign is not currently known.