Retirement age is when the Lifetime Planner will start withdrawing automatically from your savings to fund cash shortfalls. In the Lifetime Planner, you may continue to work and save after retirement. But in general, the earlier you retire, the fewer years you save and invest for retirement and the more years of retirement you'll need to fund.
Life expectancy is how long you expect to live. The longer your life expectancy, the more years of retirement you'll need to fund.