First, about that age thing. When I turned 70 I was in a small harbor in the Abacos about halfway through our ~5,000nm journey from Lake Ontario to Key West to the Bahamas. Two years later I'm about 1900 nm into another journey from Lake Ontario, down the St Lawrence and on to the Bahamas. There is no mandatory retirement age for sailing.
It is however, somewhat mandatory to keep yourself in decent physical shape and to outfit the boat so that the loads and physical requirements are reduced. This might mean smaller sails, electric winches, heat, and so on.
30' is a good intro to cruising size. Easy to manage, big enough to feel comfortable and be able to stand up to put your pants on. It will also have the basic systems you will need to learn, like freshwater plumbing, sanitary plumbing, refrigeration, inboard diesel, and electrical system. A few years of cruising will teach you whether this is what you want to do.
There is also a trade off with boat size, a 30' boat will have greater loads than a small day sailer, however the day sailer will require you to be much more nimble.
Finally, if your boat is simple enough to rig that you trailer sail it, then it will no big deal to pull a couple times a season to trailer to some new location. Meanwhile it is sitting in the slip ready to sail as soon as the ice and beer are in the cooler.