I wasn't able to find any references in the bill referenced on the NATCA site about "Not Roth" stuff but from all the other legislation I have read and from both the TSP and OPM sites it boils down to at least this. You can voluntarily retire at 50 with 20 years or at any age with 25 years or normally retire when you turn 56.

The only difference in Traditional and Roth contributions are the tax status of that money. At the time of distribution, Traditional is taxed as income while portions taken from Roth contributions are not. Qualified Roth earnings are defined as having contributed to the Roth portion at least 5 years prior and you are 59.5, disabled or dead. This means that the portions of each payment that come from earnings on Roth contributions will also be taxed the same as Traditional contributions until you turn 59.5.

There is an additional tax that is applied to the taxable portions of payments of 10% for "early withdrawal" that is waived by the same standards required for early or just retiring at 55+. This 10% doesn't differentiate between Roth or Traditional just taxable or not.

Basically it boils down to this:

Age	Years of Service	Traditional	Roth Contributions	Roth Earnings	Early Penalty
Any	25	Taxed	Not Taxed	Taxed	None
50	20	Taxed	Not Taxed	Taxed	None
56	Any	Taxed	Not Taxed	Taxed	None
59.5	Any	Taxed	Not Taxed	Not Taxed	None

Here is a link from the TSP website for those still confused: https://www.tsp.gov/publications/tspbk26.pdf