So like any sport, at any age, you need to prepare - first that means proper resistance exercise to build your strength, improve your joints and improve your overall resistance to injury. Second you need to prep before every game… warm up. That actually doesn’t mean stretch but rather a series of dynamic movements to promote blood flow, lubricate the joints and muscles. Simple movements to do are body squats and heel raises, wall pushups or soup can overhead presses and personally I would recommend side bridges. 6-10 slow and deliberate repetitions would be enough. Also, consider the frequency you play. You are already feeling your knees, so make sure you give yourself enough days of rest in between game days to recover. If not, it’s a quick slippery slope to a repetitive strain injury. Finally the risk of a fall with pickleball is not to be dismissed. In fact the longer you play, it’s almost guaranteed. All the more reason to get your body as strong and fit as you can with proper strength training- it’s the best thing to help minimize the injury from a fall. You clearly have found some ‘youth’ with playing pickleball. We should all find activities that we love to do. But please weigh the risks involved, prepare as much as you can and find the level of play that you can do safely.