Hi Physical Wreck
If you play golf, walking running and cycling at 44 you can't be that much of a wreck so keep going! However I dare so you'd be playing golf in a lot of snow at the moment! BRRR!
Yes there can be a number of causes of pain on the lateral side of the knee. Some common things you will find in your age group are:
Option 1 Lateral meniscus pain - this is usually due to the meniscus starting to break down a bit and the pain and tenderness is usually right on the joint line. Conservative mangement - getting the knee stronger particularly the quadriceps muscle - the muscle in the front of your thigh that you squat with, straighten the knee with and do things like kick the caddie with when you fail to score. this usually is best done with something like a leg extension weights machine at the gym (you would need something quite high intensity if you are quite physically active and getting some advice about this. If it really doesn't settle you could get an orhopaedic surgeons opinion but I would recommend avoiding considering the knife to start off with
Option 2 is an iliotibial band problem which may be causing an irritation of one of the the bursa (slippery cushion of lubricant that lies between tendons) or irritating a tendon itself. Iliotibial band problems are quite common and may be due to to much tightness of the one of two muscles around the hip. You really need to get a physio to look at this. Often there may be a concurrent weakness of the medial part of the quadraceps muscle. specific strengthening and stretching exericses can fix this.
Option 3 is you could be your lateral hamstrings tendon (biceps femoris) causing problems but this much less likely on a squat.
It is unlikely to be a ligament - that usually requires and inury.
Probably worth spending your money and going to see a good MSK or sports physio who can sort it out for you.