Has he had any bloodwork recently? I do annual "senior" checks on mine which include thyroid and major organs starting at 7.
If that all checks out, can you find a new "job" for him? My almost 9 yo started getting a little quieter recently, and I decided to take back up tracking again after several years in part to give her a job. She had a good foundation at it ~7 yrs ago, and wow, I've got myself a 2 yo again. She's very happy to be back to work. Had her in for her annual bloodwork this week and all came back perfect and the techs were all laughing at how animated she was. Anne