[weinzierl]

I still have a DynDNS (later Dyn and then acquired by Oracle) account.

It is a bit funny since the "Dyn (company)" Wikipedia page[1] says the company was founded in 2001, but I'm pretty sure I had this account already when years started with 19.

[1] https://en.m.wikipedia.org/wiki/Dyn_(company)

EDIT: Not an online account, but I only had a single mobile phone number my entire life.

[gwbas1c]

I attended a talk by the founders in early 2004. It was a non-profit hobby project, so it may have existed in some form before 2001.