I think it's an ego massage as others have mentioned.
A man established financially and in career and life can "rescue" a younger woman...like the proverbial knight in shining armour. Maybe the feeling is they'll be easily impressed with his achievements. And swoon over their sage life experiences. 
I've achieved everything in my life singlehandedly so at 45 I wouldn't really fall for that bullshit if I'm honest.
Then yes it's a status symbol of virility to have a fresh young woman on your arm.
When I first became single in my 40's I had quite a few propositions from guys in their 20's. Not for relationships but for sex. It wasn't even pump and dump (beautiful as that thought is) but a big fantasy to be with a woman who knows what she wants and doesn't give a shit about getting down to it.
When I think back to my 20's I spent most of my bedroom time covering up my chest because my tits were too big, faking stuff because I was under confident and generally putting on a show of sex because I was lacking in experience. I was at my most beautiful, but I didn't enjoy the experiences as much as I do now I know myself.,
My DP is 6 years younger than me and my age really turns him on. The only tiny ego boost I get is that it annoys my ex that he's nearly 10 years younger than him. 

