Young girls date older guys for a few reasons. . .
1) Older men
seem more experienced in life, secular activity, philosophy, preference, etc. . .
2) The appeal of dating a person who's apparently more mature, although a lot of guys just age, and never really grow up. Some older men thank their lucky stars for the never-ending supply of inexperienced teen girls who they can sleep with, and also that these girls aren't as demanding as . . . well, mature women.
3) The showy display of it. Some girls like the image of being seen w/ an older man.
4) Like a bunch have already said, most older guys are more financially stable, and a lot of young women see an older man w/ money as a win/win.
5) Society used to portray the ideal couple as a man who was somewhat older w/ a younger, innocent woman as his partner. That's not how it is anymore in our modern society(older women date younger men more frequently now), but I don't think that the mindset has fully left.
Then again, maybe some girls feel that older guys are more experienced sexually. I dunno. The reasons probably differ w/ each person.