Could this be Starters (2012) by Lissa Price...?
A synopsis from BookTrust:
Callie and her little brother exist in a futuristic world in which chemical warfare has killed everyone aged between 20 and 60 years old. Only the elderly (Enders) and the very young (Starters) have survived.
While grandchildren of rich Enders live in luxury, young orphans like Callie are forced to eke out an existence as starving squatters in deserted buildings - and if they are caught, they will find themselves condemned to an Institution.
But the Body Bank offers a promise of much-needed cash - Prime Destinations pays the teenage Starters to rent out their bodies to wealthy Enders, giving them a chance to experience being young again. Yet for Callie, this chance to quickly raise some money soon becomes even more sinister when she discovers her renter intends to use her body to commit a murder.
This bleak dystopian novel makes a compelling read, grabbing the reader's attention from the first page. Although this story reaches a satisfying conclusion, a sequel is also anticipated.