Is it a good practice to answer old unanswered questions? I've seen some old questions with no answers and am assuming it is fine to answer them. Also, is it bad to do so a lot?
I've seen some old questions with no answers and am assuming it is fine to answer them.
Yes, it is. There are even badges to encourage such behaviour: Revival and Necromancer. The latter can also be awarded on old questions which do already have an answer. There wouldn't be any badges if we wanted to discourage this behaviour.
Also, is it bad to do so a lot?
No. A good answer is welcome to any question, whether old or new. I can't imagine anyone complaining about too many old questions on the front page because finally somebody took the time to answer them. (Probably also because it takes a lot of time to find and write good answers to a dozen old questions.) This is unlike edits to old posts, which have limited value, so they need to be done in moderation.