I've seen first hand what happens when you wait til they're older - my cousin was 16 as his mum was too scared or afraid to have it done - and it didn't work.
Everyone I know of that has had it done when younger is perfect! I need glasses while driving or watching a movie - but many other people my age are exactly the same!
Honestly all I remember is the gunky eyes when waking up in the morning for a couple of days. I thought it was 'cool' though (my siblings thought it was so gross it was 'cool', haha)
Apparently I weirded out my brother as I started looking at him straight from across the dinner table, he was expecting my eye to wander