Gerhard Passman Paseman suggested that I post the comments I made to his post as an answer. I will edit it a bit.)
I suggest that a blog with theme exactly the question of maths in retirement might be quite fun to do. My experience is that some of the web activity which I am involved with is not being done only by full time professional mathematicians. The other contributors have good mathematical credentials and may be retired, out of work(!), or have another job which does not fully fulfill their mathematical interests and they can thus be freer to contribute when the political pressures of having to publish work might otherwise dominate. People who have retired whether from (school) teaching, from lecturing or from industrial mathematics have experience and knowledge that if pooled could be useful for everyone.
As some of you may know, I was `retired' by my university closing the mathematics section in the University of Bangor, but I still do a lot of research and contribute to the n-Lab etc. Retirement does not mean that you stop doing maths if you want to (we all know it is an addiction!) or if your background is in secondary school teaching or in business or industrial mathematics,, that you can not start building up mathematical activity of various sorts. I would not know how to start such a blog, so will not volunteer to do so, but would encourage others to try it out. The exchange of ideas problems etc. could produce some very interesting results.