Oh where do I start! Being in the punk scene I'm regularly around such bands. For a start, 2 members of one of my bands are over 50 but I doubt you'll have heard of them! We're playing with the UK Subs this week though so there's one for starters. Charlie Harper is still going strong, what a legend.
Last weekend we played a festival up in Derby with bands such as The Men They Couldn't Hang, Conflict and Discharge; all still going strong.
Other bands off the top of my head such as Drongos For Europe, Cocksparrer, Sham 69 (both lineups!) and Infa Riot have also still got it. If anything, 'Sparrer just keep getting bigger!
I'd have to disagree about SLF though, they were great at Rebellion a few years ago.