What treatment options are there for a 2-year-old blood clot in the femoral and popliteal veins?

Depends. This depends in your symptoms. Compression therapy helps with swelling, pain and even ulceration. This can be in the form of stockings or bandages. There are other options but you should see a vascular surgeon.
Too Late to Treat. It is too late to treat those clots. The most important thing you can do is prevent new clots. This would include blood thinners if your physician feels they are needed. I would recommend to wear graduated compression stockings anytime you fly or travel long distances. Graduated compression stockings can help prevent post-thrombotic syndrome which is blood going the wrong way in the deep veins.
Lots of clots. It sounds as if you're describing "deep venous thromboses (dvt)". Unfortunately, treatment at 2 years is typically aimed at management of clot progression or embolization (travel). Blood thinners are typically used long term, sometimes "filters" are used additionally to prevent travel and rarely is surgical extraction performed. Dissolving a clot (thrombolysis) is usually done only emergently.
Support stockings, First question is do you have hypercoagulable state. If not then just support stockings for ever. They sign. Reduce risk of post phlebitic syndrome which creeps up on you slowly and by the time you know you have it you're screwed. So wear 30-40 thigh high support stockings when awake for life.
Many answers. As many have have, it is probably too late to treat the clot but you might not have to. The first thing to know is whether the clot is still there. Even if the clot is still partialy present, you may have developed enough venous bypass routes that the clot isn't blocking flow any more. Getting an ultrasound is important. I agree that you need to be in 30-40 mm hg compression stockings for life.