It looks like T-Mobile 55+ plan doesn't qualify. But for those that are on a regular T-Mobile One plan, this is your lucky day.
https://newsroom.t-mobile.com/news-and-blogs/tmobile-uncarrier-netflix.htm
T-Mobile (NASDAQ: TMUS) today unveiled the company’s latest industry-changing Un-carrier move: Netflix On Us. Through an exclusive new partnership with Netflix, T-Mobile ONE family plans will now come with Netflix — at absolutely no extra charge.
https://newsroom.t-mobile.com/news-and-blogs/tmobile-uncarrier-netflix.htm