Is Vegeta older than Goku?
There is no doubt that Vegeta is older as Goku was only an infant (about 0-1 yr old) when he was sent to Earth, while Vegeta was already fighting in another planet (about 5 yrs old), so Vegeta is about 5 yrs older than Goku.
Could Android 16 have killed Goku?
In Xenoverse 2, Android 16 reveals that while he is programmed to kill Goku, he recognizes that Goku is a noble person and admits that he would prefer to be free of his programming.