Last Christmas I realised that my brake fluid hadn't been changed for nearly 6 years, so I set to with my trusty Sealey pressure bleeder, expecting horrible brown gunk to come out.
But the old fluid that came out was as pristine and clear as the new stuff that went in. The foot pedal is a maybe bit firmer with the new fluid, but that's about it, I haven't noticed the braking being particularly better.
I wouldn't say not to change every 2 years, it's a quick, easy, and inexpensive job and good for peace of mind, but I wouldn't fret if it was a bit longer than that.
