I can have a 1litre jug of water that is 80% full as that is 800ml.
If my knee is 80% good what does that mean? It’s impossible to quantify. One persons muscle fibres and ligaments are completely different to someone else.
Only you know your body. If it hurts stop doing it as that is your body telling you something. If i were you i’d look at building up muscle in the legs in a non-impact way first so there is plenty of muscle to hold and support the joint and look at your diet to ensure you getting enough builidng blocks for muscle and bone, but i am certainly not medically trained that is just an opinion based on bits i’ve read and some sort of logic.