Are you looking for a cosmetic solution, or trying to fix decayed and broken down teeth?
The first question should be, "should you get Lava crowns for your front teeth?" Lava is a very strong porcelain material, but perhaps not the most esthetic choice for front teeth. There are other choices of porcelain that well-versed cosmetic dentists can help you with.
As far as when...in the world of dentistry you are an "adult" at about age 16, when most growth has slowed down significantly. The front teeth are mature enough to receive crowns (ONLY when necessary) as early as then, but each patient is different.