the 2.2g per kg bodyweight is the "more", it's a good target at all ages because most humans with regular diets are way below that. the 1g per pound has been around for a while and it covers the upper ceiling for maximizing protein synthesis in weight lifters. But even for non-weightlifters the higher protein intake can stimulate muscle growth, which is really important as you age because the human body develops anabolic resistance, meaning muscle synthesis slows down and you have to counteract it.

In any case going beyond 2.2g/kg/day is almost always overkill and wont help, but reaching that amount is beneficial at every age, and more important at old age.