I’m a doctor and a soccer player ;-) Most likely, your muscles are adapting to the novelty of playing soccer after being primarily a runner. Arthritis at your age is very unlikely. There could be multiple issues, or just the fact that you need to give your body time to learn movements. Even now, when I haven’t played soccer in a while, when I first start, I get sore all over and it can take months of training to feel “normal” again. Point of reference, I just started a new season a few weeks ago, and after the first game, I could barely walk all week. Don’t fret, it will get better with time, but a doctor’s visit should exclude anything serious.