From the sounds of it, your account would be on the “original” Runescape 3, rather than the Old-school Runescape this post is about.

Old-school Runescape is essentially a fork of a random backup they found of the game as it existed in 2007 that they released in 2013 after a lot of dissatisfaction about how Runescape had changed over that timespan.

None of the accounts/characters from the original game were migrated.