Seven financial planners, wealth managers, and personal-finance writers offered advice to younger people on preparing for retirement.Getty Images; Jenny Chang-Rodriguez/BIMany of the 3,300 older Americans BI heard from recently regret not preparing enough for retirement.Financial planners described how younger people could set themselves up now to retire comfortably.This is part of an ongoing series about older Americans' retirement regrets.For many Americans, their golden years can be a time of reflection — and regret.Since mid-September, more than 3,300 older Americans have shared their retirement regrets with Business Insider through a reader survey or direct emails to reporters.