I'm about your age soon
Also played a lot in my teens, then took a break in my late 20's and then started again 4 years ago.
My knees hurt, and I have to cut down on the number of times I play tennis a week - maximum 2 times a week now.
You have to do certain things to be able to continue playing tennis in my view.
Avoid hard courts - I'm serious AVOID HARD COURTS !! They are very tough on your legs and will destroy you in the long run. Find a place where they have clay courts. Continue on hard courts and you're done in 4-5 years time.
Start playing doubles more, practice on the wall more often and just hit with your partners instead of playing actual matches. Matches are very tough on your body in the long run, so try to cut down on that.
Think about the racquet you use, the strings and how you hit your shots.
Do this to minimize the strain on your arms and body.
Why are there so few clay courts in the US, when all you can find in Europe is clay courts ?
Clay is sooo much cofter on your legs and body.