Is this a good website for a mature adult who picks up new topics quickly to self-teach chess?
No, it's not, but it might still be very beneficial to you. (Chess) Stack Exchange is a question and answer site, so:
You should only ask practical, answerable questions based on actual problems that you face.
(taken from here).
So don't expect any tutorials here, or the possibility to play an actual game against someone. However, browsing through the site you will find a lot of resources which might help you - this question for example. If you need a resource on a specific topic, and nobody has asked it before, please go ahead and ask for it.