Depends on a few factors. How gentle are you when you handle a piece. Products are important. No shampoos with sulfate, no products with alcohol.
I use a daily leave in conditioner. I only wash the piece twice a week. Longevity is also dependent on the base material. I do get about 6 months from a Swiss Lace piece. Using knot sealer can help as well. As they say your mileage may vary. Of course the quality of the piece is first and foremost.