H1B extension after 6 years of original petition date

Hello Friends,

     My bro got H1B stamped 3+ years back, but he didn't travel in first 3 years. Then his employer processed cap exempt H1B petition and now he has started working in US. His H1B visa is valid till 30 Sept 2017. Since he was not in US for complete 6 years, is he eligible for extension in 2018 H1B processing ?

     Appreciate your insight / help this his case. Thanks in advance !!

With Regards,

Your Friend.