I don't connect to Twitter, but I thought that LibsOfTikTok posted evidence in the form of screenshots and recordings of what hospital representatives had said over the phone. Someone even found a paper where authors affiliated with Boston Children's Hospital reported 65 gender affirming surgeries performed when the patient was a minor at the time of surgery: https://doi.org/10.3390/jcm11071943 (Table 1).

From the paper: "The Center for Gender Surgery (CfGS) at Boston Children’s Hospital (BCH) was the first pediatric center in the United States to offer gender-affirming chest surgeries for individuals over 15 years old and genital surgeries for those over 17 years of age. "