Hi.
As per the details given by u and according to your age degenerative changes or as we call it arthritic changes are less common.
But muscles surrounding your knee joint can loose their strength at any age due to inactivity or overload.
The main muscle effected is quadriceps I.e thigh muscles and adductor muscles I.e inner thigh muscles.
Next Steps
start doing stretching exercises for knee
isometric exercises
reduce weight
(under guidance of a good physio).
Health Tips
cycling and walking
heating will help.