Your oldest friend knows versions of you that your newest friend never had to forgive.

Old friends carry your drafts. They were there for the version of you that was careless, or unkind, or ridiculous, and they stayed, which means the relationship contains forgiveness that never had to be requested from anyone newer. A new friend meets an edited person and has no idea what has been left out.

Both kinds are worth having and they do different things. If you have someone who knew you early, that is a rare form of being known and worth maintaining actively. And it is worth remembering that your newest friends are meeting someone the old ones helped build.