To begin with, withdrawals from traditional employer-sponsored retirement plans like these fall under the Internal Revenue Service's "required minimum distributions" (RMD) guidelines. (You aren't required to take these distributions from a Roth IRA.)
First of all, save early – and save often. Too many people put off saving for retirement until they are in their late 40s – and even their 50s. If you wait until you are in this age group, you can still do quite a bit to help build the resources you will need for retirement – but it will be more challenging than if you had begun saving and investing while you were in your 20s or early 30s.