You can use the same account. One account can access Old School RuneScape, RuneScape 3, and the forums. However, even though your profile is used across systems, your actual PLAYER ACCOUNT is not shared. Old School and RS3 are two completely different games, and share no cross compatibility other than your account you use to log in, and your membership.
RS3 is the ORIGINAL RuneScape, so when Old School used to be the only game, and eventually turned into RS3, all account data was migrated over to the newer RS3, and "Old School" (or RS2 at the time), ceased to exist.
Many people were unhappy with the new RuneScape, and after some time, they eventually brought the old version back online from a 2007 code base they had found. The engine and game was far to different from the new version to have any sort of cross compatability, so anybody who wanted to play "old school" had to start from a fresh account.
I was annoyed myself at the fact of having to start over when all my levels in RS3 were 90+, but it was kinda like experiencing RS all over again from a clean slate. Even though my RS3 has high levels and a lot of GP, I prefer playing on Old School now, and haven't played RS3 in a long time.
It's up to you whether you want to put the time and effort of restarting in old school, but while I found it daunting at first, I'm glad I did. I'd suggest just giving it a try. Knowing the game (even from rs3) will give you a much quicker start.
26-May-2021 19:09:55