Hi @theyarereallytakingthepissnow. I am the same age as you, now (sort of) on wk8.
The good news is that it is unlikely that your knees are just knackered. But there is quite a long list of things that could cause the pain such as: shoes with poor cushioning, tight muscles, weak glutes, too much pavement stomping particularly if you were carrying extra weight or when getting too tired.
In any event, you should be wearing better trainers, suited to the terrain you run on and ideally also your gait. I love my Hoka One Challenger ATR as they allow me to do both trail and some road, have good cushioning for a trail shoes, and because of their odd shape allows your foot to propels you forward properly.
When I was early 40s I did some running on pavement and had persistent knee problems. Like you, I was largely relying on my determination, rather than my body. I stopped in the end after trying various knee braces etc.
This time I lost a lot of weight first (25 kg gained since my 40s) which may not apply to you. I know my legs are quite strong from daily walking on rough, hilly, ground for years. I still do squats etc to further strengthen my glutes. So far, so good. I'm running up to 40min now.
I strongly recommend doing some strength work if you're not already doing that. Weak glutes cause many people non-obvious problems when running.
I've also had to look up some stretching videos as a 5 minute cool down walk would not be sufficient to stop tight muscles. I now need to do correct stretching before and after every run. I do what I think is needed and then do some more. Quite tedious really but sadly I think a sign of my advancing years.
I also minimize the time running on pavement, which I appreciate may not be possible for everyone. Particularly when I get tired, I really notice the greater impact in my joints on a hard, unforgiving, surface. Again, this is where good shoes will help a lot.
If you do run on pavement it would be worth getting a gait analysis so they can recommend the right shoe for you.
Lastly, well done!