User blog comment:B214/Question and Answers/@comment-79.49.169.68-20121231205007/@comment-1359322-20130101093121

Also the use of the Boosted Gear itself does not reduce one's lifespan, it is the Juggernaut Drive that reduces ones lifespan such as in Issei's case his supposed lifespan is 10,000 but got reduce to 1% that is 100 years upon activating the Juggernaut Drive.