Why Does My Cat's Nose Turn Brown On The Sides?

Most kittens are born with a lighter coat.  Even their stripes will be less pronounced when they are young kittens (6-12 weeks).  As they get older, their fur will darken and the stripes become darker.   

Many brown tabbies are born a very light tan color, so light that they actually look grey.  Actually, each hair has three to four colors on it - white, grey, tan/brown, and black.  Because the fur is still short, the light tan / grey part of the fur stands out, but this will change as the cat's coat grows longer, thickens and matures.

If he's a outsider cat he may just have a sun tan. Otherwise I'm not sure.

If your cat is leaving Early child hood its normal but if it is rough and dry, wet a cloth and wipe its nose if condition persists take the cat to a vet