The whole relationship is gross. Sara clearly has a father issue, and is looking for that type of support from an older man. As a replacement father. Any psychology book will tell you that females with an absent father figure often seek the attention of older men. It has always been like that, sara trying to get grissom's attention so he can 'discipline' her. Nasty.
If that were true, why did Sara date Hank - a man her own age? Why did she flirt with Greg, Nick and David - men roughly her own age? Why did she flirt with Mikey - her own age?
If anything, Grissom has been shown to be the exception in her tastes, not the rule.