Lanefan
Victoria Rules
By "group" I assume you mean "the same core people who game together on a regular basis regardless what campaign or system they might be playing".
On that basis the core group I'm in have been at it for 30 years as of this coming April, running various different campaigns (mine are in my sig.) using the same 1e-homebrew system. Which means in May my answer will tick up to the next option...
A secondary group with lots of personnel overlap that plays 3.xe hits its 10-year point in about 3 weeks.
Lan-"yeah there's gonna be some celebrations this year"-efan
On that basis the core group I'm in have been at it for 30 years as of this coming April, running various different campaigns (mine are in my sig.) using the same 1e-homebrew system. Which means in May my answer will tick up to the next option...

A secondary group with lots of personnel overlap that plays 3.xe hits its 10-year point in about 3 weeks.
Lan-"yeah there's gonna be some celebrations this year"-efan