Yep, good advice in terms of the habits that you want to be learning and practicing. An occasional lesson from a decent teacher will keep you in the right direction, but you can also do some of your own research/reading to better understand the game's tactics as well as the fundamentals that you need for good strokes, etc.
Network as much as you can to track down potential hitting partners - teaching pros may be able to give you some good guidance in a new setting and you can also make some tennis pals at clinics and organized functions that are appropriate for your level. You could also try touching base with local high school or college coaches to see what they know about the "goings on" in your area.
You're certainly not too old to go pretty far with this sport, especially considering that you'll have it forever - other sports careers can often end after the high school or maybe college years, right? Yeah, it takes a bit of time to get proficient, but it's awfully rewarding after you stick with it for a while. With the right work and guidance, you can certainly progress to a higher level in terms of the NTRP ratings. Involvement in tennis can be good for you socially and your pursuit of a higher level will also encourage you toward better general fitness.