The oldest xda members (not by age but by membership) I personally know and who are still active today are:
- MikeChannon (join date June 7th 1972 is like a joke, not sure of the real join date, maybe Sept 2006?)
- the_scotsman (join date: January 30th 2006)
- malybru (join date: August 17th 2006)
The founder of xda is Peter Poelman (join date: January 19th 2003 but he's inactive since 2010)
Found him: Peter Poelman but inactive since 2010. Found more recently active members like @MADmanFREE (2015) or @Gene_uk (2016) and even @richardyates (2020) but none still active today.
Ironically we have the same concern 2 decades later but about a multitude of gigabytes instead of 128 megabytes (possibly 128TB soon?)