How much are people saving for retirement by age?  KCRAAverage 401(k) Balances in Your 50s: How You Compare and Factors That Influence Your Savings  Yahoo FinanceWhat Americans 75 and Older Typically Have Left in Retirement Savings—By the Numbers  InvestopediaHere’s the Average 401(k) Balance of 44-Year-Old Americans (How Do You Compare?)  FinanceBuzzIf You’ve Saved This Much for Retirement by Age 35, You’re Ahead of the Game  The Motley Fool