@dkapustin I went to a PT for hip bursitis this week and while there had him measure the flex in my knees. The one done in October 2017 is stuck at 115, the one done about five years earlier is at 125, and it was only at about 120 a year and a half ago, so it can improve apparently.
The therapist said it is more important to be able to get to 0 degrees than to get to 120 or more, because if you can't make your leg totally straight your knees can buckle. How is that number for you?
I just did some googling and found this. I do not know how reliable the site it is from is though. You can function fairly well with 115, I am proof of that.

"Range of Motion Basics After Knee Replacement Surgery. ... A fully bent knee will max out at about a full range of motion of 135° degrees of flexion. As a general rule, a knee flexion of about 125° will allow you to carry out most normal activities. For daily living, a minimum flexion of around 105°-110° is required. Jul 5, 2017"
JK