need help on a sister search

I recently found out that I have a sister that was given up for adoption in Tennessee, the information i have is her original birth certificate, which only lists the mother, (but due to adoption services by what is now catholic charities, i believe the father's name was also mentioned in whatever documents exist), and various communications and papers from hospitals and legal papers etc...i know just about everything except if her name(s) were changed, and the adopting families names.now, do i need to wait to attempt contact the same as if it was the birthmother? though i'm 25, i believe she will just be turning 20 in october... and i'm unsure about what can be done on my end to contact her (if she's willing, of course) in that she's under 21, but over 18, so I'm not too clear on the exact laws involving siblings. can anyone give me some advice?