Water Wetter

There's no air flow through radiator at stand still so that's why the fan comes on and off
It's doing it's job mate I wouldn't worry about it

 

Its even more annoying on a full sports bike at traffic lights on a 35-40 degree day. You get super heated forced air thru the fairing, toasting ur nuts and making it feel like some kinda wet fart has occurred that u knew nothing about. The time to really worry is when the fan doesn't come on at standstill. (cuz that's really expensive)

 

Wouldn't hurt to change the coolant anyway mate and don't forget to use de-ionised water as well
Perhaps in the past someone has used tap water and the radiator might have a bit of furring which could restrict the flow causing the temperature to rise quicker than normal?
The fan operating quicker than expected could be an indication of this therefore suggesting the fan is ok
You could flush the system before filling with the right mix

Or just ride on really really cold days
(Sorry couldn't resist )