How long does the effect of Botox last after a single injection?

I heard that in the case of Botox, the effects are somewhat semi-permanent.

So, I'm curious how long the effects of Botox last.

Also, once I start getting Botox, do I have to get it for the rest of my life for it to be effective?

Are there many people who get Botox even at a young age...?

Or is there a separate procedure that is good for a light treatment instead of Botox?

I'm worried because I heard that although Botox is effective, there are actually quite a few side effects.

Also, are procedures like Botox painful?

My face has been sagging lately, so I've become really interested in procedures like Botox.

I'm so jealous of people with firm skin.