TSP Withdrawals after retiring before 59 and 1/2 years

Good day,

I've been in the military for a while (I am like 16 – 15 years away from the 20 years active duty service) but I do have a question: I've been contributing moderate-aggresively to my TSP since last year and I do have a question to see if I want to do 20 years active or just 20 years ative/reservist: If I do 20 years in the active duty, contributing Roth, and let's say I would be like 50 years, can I start withdrawing my contributions without any tax penalties? Or if I serve 20 active duty I will need to wait until 59 years and a half so I don't have any tax penalties? I've been trying to do my research on that matter but I haven't been able to see an answer since most people doesn't do 20 years active duty. Thanks for any information you all can provide me.