I recently processed a 2 year old rooster and after resting for several days, popped him into my Instant Pot. After the standard 30 minute cooking time, I poked a thigh with a fork: still tough. No problem! I just cooked him for another 30 minutes and he was as tender as a young cockerel...but...
The reason to get a pressure cooker is to cook tough meat, and your rooster fits the description!
Here are the pages of my recipe book relating to pressure fried chicken:
I did the last page sideways to try to get more into the scan, it looks funny but I think you can print it better. There...