Interesting article — What's protein, why do we need it, and how do you get more?:
The average adult needs about 0.8 grams of protein per kilogram of body weight - so a person who weighs 80kg needs about 65g of protein per day. … We also need more protein as we age - about 1.5g compared to 0.8g.
Our fancy new bathroom scales have revealed I don't get enough protein, so I'm working on that.