I had my knee first done at 58. Back in 2014, 58 was considered "on the young side", but there was no other option. To me, it's not about age, it's about life. If your knee is stealing your enjoyment of life away, then now is the time to do it. Life is for living, and if we can't walk, we can't participate.
As others have mentioned, the implants of today have a much longer "shelf life" than in the past. While no one can guarantee you'll never need another one, you have a better chance today than even 10 years ago.
I say, if your quality of life is gone, or nearly so, due to not being able to walk, or not being pain free when you walk, or similar, then don't even consider your age, just what you want out of your life now, and in the coming years. Do you want to sit on the sidelines more and more as your knee worsens? Or do you want to get the surgery and recovery behind you and begin the process of taking back your life? Only you can answer this, and only you can decide.