Ex-NFL Star Brian Westbrook -- I'm Still FASTER Than Most Pro Running Backs!

He may be retired, but former Philadelphia Eagles running back Brian Westbrook says he's still a SPEED DEMON ... and could put up a 40-time that's faster than most pro backs.

In fact, the 34-year-old tells TMZ Sports ... he's FASTER now than he was as a rookie in 2002, when he clocked a 4.57 at the NFL combine.

It's unlikely Westrbrook is thinking about coming out of retirement at this point, but if he's telling the truth ... he would make a HELLUVA flag football teammate.