One of the local doctors who refer's patients to us says that the only thing you can blame on old age is gray hair and wrinkles, and I tend to agree. There is some degredation due to normal use, but it is minimal. Most of the damage we do to our bodies comes from abuse or misuse. Doing too much too fast or doing things we have no business doing in the first place. As far as the meniscus repair, "Too old" simply means that you aren't an elite level competitive athlete at or near their prime, which is what I am routinely told is the criteria for going to the trouble of repairing a meniscus.
Keep us posted on how your surgery and subsequent therapy goes.