I had my right knee replaced almost 3 years ago, at age 57. The recovery was tough, and very painful. I fell into a mild depression, which was a complete first for me, and came as a surprise. The experience was humbling.
I very much agree with Rich99 about the importance of pushing your exercise routine. As you heal, scar tissue forms around the knee replacement. It is important to keep breaking up this tissue, otherwise the ROM (range of motion) of your new knee will be limited. The physician's assistant gave me great advice, by telling me to make pain my friend. He advised that, especially for the first 6 weeks, I should make doing the various stretching exercises my full time job. This didn't mean that I should be doing them all the time, he said, but that my whole day should revolve around either doing them, or icing and relaxing, and planning for when to do them next. He told me there was a way to mentally disassociate myself from the pain. There was a knack to it, he said, that would come with practice. He was right; it did. As Rich99 said, the first 6 weeks is critical. You can still achieve increases in your ROM after 6 weeks, but those gains will become increasingly smaller, and will be harder to achieve. Do not slack off in the first couple of months, whatever you do!
There are many exercises that can increase your flexion (bend). As an example, the one that worked for me was to sit on a chair at my desk, and use my good leg to push my bad leg as far as it could bend before the pain kicked in. Then I pushed it a bit further, and held that position for 10 minutes. To distract myself, I'd look at stuff on the internet - a useful by-product of sitting at the desk! I performed this stretch 6 times a day, for a total of one hour spent with my new knee bent. Gradually, I found that the new knee bent more and more. It was encouraging, and inspired me to continue to push through the pain.
Many of the other extension and flexion stretches also involved holding a position for 10 minutes. While doing so, I'd either read a book, or look at my phone or computer to help pass the time, to distract myself from the pain. I'd place my stationary bike in front of the computer monitor and watch videos while pedaling. Although my recovery wasn't easy, there was a familiarity to the daily routine that acted as a comfort. It wasn't all torture!
Incidentally, my PA said that, generally, his older patients had easier recoveries. I am guessing this is because younger patients heal faster, and tend to create more scar tissue, necessitating more work to keep it at bay. In my opinion, the most important PT is not the stuff you do during visits, but the stuff you do at home. I only went to PT once a week (for about 6 months). The visits acted as inspiration, a source of new exercises, and a yardstick to help measure my progress. However, the real work was done every day at home.
I live on my own, and had no help during the recovery process. It can be done. My new knee feels great!