Heaps of good advice here already.  Most importantly for me is to take your time, do as much research as possible and keep asking questions.  Many of us have been ripped off or taken for the proverbial ride when it came to buying our first machine.  It was after that when we had to start fixing things that we stumbled across forums such as Aussie Pinball.  So already you are a massive step ahead of most new guys to the hobby.

You have waited 40 years so another few months won't hurt.  Shortlist the type of themes you are interested as well as whether you want all the bells and whistles i.e. a DMD machine or more of a classic style machine, these being EMs (electro mechanical) and SS (solid state electronic machines).  Don't forget to see what your son and grandkids like as well.

Also be very prepared to fill your allotted room with machines.  They tend to breed very easily and very quickly once the bug has bitten.

Best of luck with it and keep asking questions.