I just bought a nisson altima 2005 the owner advised me I need the brake fluid flushed before winter... Is this normal

Brake fluid absorbs moisture, and this can rust the insides of the brake system. The moisture was not that big of deal 10 years ago, but on ABS brake systems of today, the rust and other debris that accumulates in the fluid can do lots of internal damage, and can be very costly. Brake fluid can also break down over time from excess heat that is created from within the brake system.
Is recommend flushing the brake fluid system about every 30,000 miles, or at 30K, 60K and 90k tune up. It cost about $90, but you can do it by yourself. To do this flush, open the brake lines located at each wheel and allow the brake fluid from the brake master cylinder to "bleed by gravity", as continue to feed new fluid to the master cylinder until the fluid runs clear at all wheels.The discharge has to be collected in 16OZ plastic bottle via a clear vinyl hose from the bleeding nipple to the bottle. It is a good idea to replace all 4 nipples with new one. They are cheap and avoid problems in long run. Make sure to use at least DOT 4 brake fluid. Make sure to use a sealed bottle. The life of brake fluid in an open bottle is one week.