We know, from the script, that Sarah was 19 at the time of Terminator which took place in May 11th, 1984. For her to be 19 at that time she would have to have been born between May 12th, 1964 and May 10th, 1965.
In Judgement Day Dr. Silberman says of Sarah that she "is a 29-year old female ...". This takes place on March 26th, 1994. For her to be 29 at that time, she would have to have been born between March 27th, 1964 and March 25th, 1965.
Finally we learn in Genisys that she was 9 years old in 1973. For this to be true Sarah would have to have been born January 1st, 1964 to December 31st, 1964.
These three pieces of information tells us that her birth date must be in the range of May 12th, 1964 to December 31st, 1964. Although it is possible that Sarah's 20th birthday was on the day she and Kyle run from the T-800, it is unlikely. Similarly, if Sarah turned 9 on December 30th, 1973 and Pops arrived on December 31st she would more likely remember being 8 when the terminators arrived rather than 9. So it is most likely that Sarah was born June 1964 to November 1964.
We learn in Rise of the Machines that she died in 1997 sometime after August 29th. This would make her 32 or 33 when she died. The only inconsistency in all of this is the date of birth on her crypt which states that she was born in 1959.
|Sarah's crypt at Green Lawn Cemetary.|
However, we are told that her friends put in the crypt in accordance with her wishes. They certainly would have known when she died, 1997, but may have had no idea when she was born. It is very believable that they simply guessed at the year she was born thinking Sarah was older than she actually was. As we will see when we get to the Chronologies, there may be a good reason they believed Sarah to be older than she was.
We also know that Sarah's middle initial is "J". When we see the three Sarah Connnors listed in the phonebook in Terminator we see "Connor Sarah", "Connor Sarah Ann" and "Connor Sarah J". We know the two who were killed were Sarah Louise Connor and Sarah Ann Connor which only leaves Sarah J Connor.