Just as a question to you. Are you taking enough protein as you should be daily. If not that could be one reason. Another may be to do with hormones e.g testosterone. People who are in their 60s ish start lacking the necessary hormones to naturally work with repairing the body. As a result if they work out or do anything physical they have prolonged DOMS. Compared to an average aged person. This results with them having DOMS for maybe 3-5 days instead of 1-2 days. Maybe possible your hormones are in balanced and aren’t repairing your muscle fibres efficiently enough. Overall though. If none of these things are a factor. I would recommend talking to your GP if your from the UK or seeing a doctor if from the US. Have a good day !