Older age (50 or older) and being overweight are two key risk factors for medial meniscal tears. Other potential risk factors studied have included patient age, sex, findings on X-rays, activity level, occupation, and a history of previous injuries.
Research has provided us evidence that it’s mostly intrinsic factors (not lifestyle) that increase the risk of the type of meniscus tears that you mentioned (medial meniscus posterior root tears</i or MMPRTs).
The four intrinsic risk factors with the greatest impact on MMPRTs appear to be: 1) increased age (older than 50 years of age), 2) female sex, 3) being overweight (higher BMI), and 4) lower level of sports activity. The mechanical angle of the knee (as seen on X-rays) was one anatomic feature that also increased the risk of MMPRTs.
These risks are important because we know that meniscal tears can leave a person at risk for early knee osteoarthritis. Knowing what the risk factors are for the tears might help us find better ways to prevent these injuries. And that would mean reducing the risk of early degenerative knee osteoarthritis.
There isn't anything you can do to lower your age but if you are overweight, a weight loss program that includes increased activity would be the first place to start. That would address two of the four risk factors. Angle of the knee may be modified if needed by using orthotics (special inserts made for inside the shoes). A prescribed program of exercise, posture, and alignment supervised by a physical therapist may also be helpful.