Is 20 to young..?

my 20 yr old sister just started datin this kid for like a month and she just broke up with her other bf right before she met her new b/f who already has a 4 yr old daughter..Well now she might be pregnant is this bad or good?? is 20 to young?? she says is she isgoing to keep it so how does she tell our judgemental mother..im not sure what to think about the sitiuation b/c my mom always holds everything my sister does against me im only 16 and my mom wont let me have a life and if my sisters 20 and pregnant im never gonne be able to leave my house some plzz help me what do i do or what should my sister do???!!??