The main problem is that my ankles are not flexible enough. When I try to squat, my heels inevitably raise above the ground so that I find myself resting on my tiptoes, struggling to keep my balance.
How about timeboxing 15 minutes a day for body maintenance? Start out just reading some articles, then watching videos, then try out your first stretch, feel sore the next day, take a week off, then try out a different stretch routine, then progress, then increase your time per day because you see improvement, and one day, out of the blue, you're squatting. What do you think?
If it's something you're willing to work at, from personal experience I know it can be improved.
I can't do that, my leg can't stretch fully. This prevents me from squatting properly.
I've been slowly stretching the hamstrings but I'm still not there. I remember having the same issues when I was a teenager.
Ankle flexibility is more frequent cause of not being able to squat properly. Hips also, but not because of hamstring.
and then the first part of of a series of more general ankle flexibility exercises you can do: [2]
The ankle part can be trained separately by flexing them, I would believe. If your heels keep raising and you really want to be able to do it, have someone take a video of your attempt and study where your center of gravity travels. It should move towards the floor in a straight line. Chances are, you are simply not extending your behind outwards enough because there are other parts of your core muscles that are not flexible enough.
It's an exercise worth practicing and should be much more popular than the typical "pushups/crunches" routine that many non-athletes do at home. (This is where I will be taken apart by someone who knows more details:) Pushups and crunches train precisely the muscles that will pull your back and shoulders forward. A complex exercise such as squats and a good extension-stretch for your back will go a long way of making office dwellers feel better.
You'd probably be surprised by what happens after years of this.
But I can't emphasize how important the point of daily routine in the article is - it doesn't take much to get quite an amount of flexibility back, but habit
Your doctor was probably right to give that advise for walking.
But when lifting weights it is a much more stable position for many, and as long as you ensure your knees track a line over your feet rather than at an angle it's not generally a problem.