Read
this thread. Pay particular attention to the 'Do you really want to do this', and 'Am I Too Old, and How Old is Too Old' threads. They cover much of what you have asked.
Remember, there is no question you can think of that hasn't been asked here before. the majority of repeated ones are covered in that thread. The rest can be discovered through use of the 'Search' facility (though sometimes you have to think laterally and use Google or similar to search Pprune!).
Scroggs