It takes 3 months for any fracture to heal. An image of the Xray would help in deciding how much it has healed. Also we usually start mobilisation by 6 weeks as the knee might become stiff. Also the patellar fracture even if undisplaced many a times requires fixation due to disruption of the extensor apparatus which in turn is examined by asking the patient to actively extend the knee. I suggest you show it to a orthopedist as 8 weeks is a pretty long time and Physio should begin or else chances of stiffness are more.

Passive slow mobilisation can be started. But be careful no force. Total healing period should be 6 to 8 mths. Total healing 1.5yrs.