That's a pretty broad statement. The definition of "obvious" is different to a lot of people, and there are a lot of things that seem obvious in retrospect that weren't obvious at the time. So it's hard to use that as a way to define troll.

As for old, if the patent is still valid, does the age matter in isolation? Sure, you can argue that patents stay valid for too long, but I don't think I can call a company a troll for using an old patent if the age alone is how you're labelling them a troll.