In cases like this the person has a “paper hang-up” i.e. when written on paper it bothers them, however in reality they could care less.
You should allow the person themselves to decide what is a “paper hang-up” vs a real hang-up. So, you can say “The person is 21, but maturity wise is older” rather than the person is 22. Its not up to you to decide what a paper hang-up is – that is THEIR choice.