Strangely, I agree Marilyn Monroe's plastic surgery worked! She is one of the few who looked better, and it was decades ago!
But mostly, once people start messing with their faces to look younger it often goes horribly wrong. I had some hair colour recently (I guess) to try and look a bit younger, but I don't really like it that much, its not me, and I think most attempts to look "younger" fail (by definition). And its not an attractive look. You can be "beautiful" and middle aged, and old for that matter. Its different from the bland face, shiny hair, bright eyes look. But it can have its charms if authentic.
As for Simon Cowell, agree, and find it really bizarre. Its not like he even "relies" on his looks in the music business, he's a producer etc. Very weird.