sentences:  This demographic trend coincided with the gradual relaxation of states' restrictive licensing laws – the legal drinking age was generally lowered to 18 (in line with changes to the voting age) and the opening hours of pubs were finally allowed to be extended to 10pm.Rock concerts were attracting younger audiences in large numbers, and changes in the licensing laws enabled pubs to begin presenting regular concerts by rock groups in the early 1970s.Such "pub gigs" were often presented free-of-charge, with the cost recouped from alcohol sales, although it became more common for licensees and/or promoters to charge an entry fee, especially for the more popular groups whose fees were higher.