At 55 you are to OLD to get into this trade. Sorry just being honest. This is a young mans trade. Yes there are a few that can do it into there 50`s and 60`s, but not many. At 51, i am usually the oldest guy in the parts houses when i walk in. Use your mind not your back. Go to school for something in the medical field. Lab tech or what every else.
But if you must get into this trade, then look for an hvac job at a school district, hospital, airport, state or city job. A job like that is more geared toward the maintenance side and less demanding on your body. Pay will be less, but my have good benefits.