Samantha is Mason's sister in the movie Boyhood. Samantha's actress is lorelei linklater.
Although her age was not told in the movie, in the start of the she had a memory of her when she was 6 years old. This means she was a little bit older then 6. The end of the movie Mason was around 18 making Samantha in the start of the movie around 9. This is giving them a estimate of a 3 year age difference. So in the end of the movie she was probably around 21 years of age.
It was never said what her favorite music was but there is some evidence. When she is younger she is seen singing Oops!...I Did It Again by Britney Spears. When she gets older she is heard listening to Lady Gaga music like Poker Face and Telephone. She even talked about seeing Lady Gaga in concert.