Pierre YuHow much money you need to retire at 35 and live on investment income alone until 90verified_publisherBusiness Insider - Written by Tanza Loudenback; edited by Libby KaneMost Americans have been in the working world for at least a decade by the time they reach their mid-30s. For some people, that's enough. With an early retirement craze taking hold in the US, you'd probably be in the minority if you haven't wondered, How much money do I need to quit my job and never …