This is a hot topic. 'Preventative' botox works by stopping you from making the repetitive facial expressions that eventually carve deep grooves into your skin. If you squint a lot, that crease will eventually become static (present even when you don't squint). Botox stops the muscle from creasing the skin, so that static line never forms. However, starting at 28 is a personal choice. You don't need much – literally 5-8 units in the crow's feet and maybe 10 in the forehead. You won't become 'immune'; that's a myth unless you're using insanely high doses every 8 weeks. Atrophy is real, but that's the point – a weaker muscle creates a smoother surface. If you stop, the muscle regains strength in 3-6 months.