Q: If I retire from the Postal Service this next year, can I draw monthly payments from my TSP account before I am 59 1/2 without penalty?
A: Yes, if you: 1. Retired during or after the year in which you reached age 55; or 2. Take them as series of Substantially Equal Periodic Payments under IRS rules; or 3. Meet one of the other exceptions to the penalty outlined in the notice you’ll find at www.tsp.gov/forms/octax92-32.pdf
— Mike Miles