Back in the day a lot of kids played on torn ACLs until they finally realized that something more was wrong with the knee. Some non-athletes just live life with torn ACLs. It used to be that people would say my knee keeps going out and not knowing there was quite a bit of damage.
Absolutely right.
I know a guy who was incredibly active as a cyclist and tennis player. He started to have serious knee pain in his early 50's. He finally went and had an MRI, and the doctor took one look at it, and asked "when did you tear your ACL?" He had no idea what the doctor was talking about, until he remembered that when he was 17, he had missed a step while climbing down a ladder, landed awkwardly, and then had a swollen knee for about 6 weeks.
The doctor told him that he pretty much didn't have an ACL. Yet he had been cycling and playing tennis for 30+ years before it really slowed him down.