When calculating GDP using the income approach how do we make sure that we count only wealth produced in given year?
So, if I correctly understand what I learned in comments, this question is resolved by two things:

1.We add deprecation in order to ignore it, rather than take it into account. It makes sense because incomes are already decreased by amount of deprecation, so in order to "unaccount" deprecation we must add deprecation. And due to us ignoring deprecation it doesn't make any sense to make distinction "deprecation of new assets VS deprecation of old assets", we ignore both of them.

2.Like renting, money lending is an ongoing service. You can keep extra money for some time, but with each year/month the amount of extra money that you're allowed to keep will become less and less.