"You can tap your 401(k) at age 55 w/o penalty. Further, you can avail yourself of §72(t)(2)(A)(iv) "substantially equal periodic payments" to withdraw from your IRA's at any age w/o penalty."

Badger is correct. It is also called ruling 89-25 and you can get a copy from the IRS, it's about a page long. I am using it as the basis for withdrawals started nearly 3 yrs ago from my qualified plans.
You can use one of three methods for determining how much to withdraw but the most flexible one is an amortization based on your life expectancy, an assumed "reasonable" rate of return and the combined value of your qualified plans.
The rate of return is not specified and my discussion with an agent led me to use 8%. He said anything up to about 12% would probably not be questioned. In addition, nowhere in the regulation does it say you cannot change the % each year!
The withdrawal period is a minimum of 5 yrs or age 59 1/2, whichever occurs later. That makes it ideal for someone 54/55 yrs old!
Good luck.