A:
Acts of the Apostles contains a brief account of Stephen being appointed a deacon of the early church and of his subsequent martyrdom, but does not tell how old he was. Raymond E. Brown (An Introduction to the New Testament) says that we can never verify the martyrdom or even existence of Stephen, in whcih case it is a moot point how old he was.
Saint Patrick died of natural causes, probably complications of old age. He was not a martyr.
Monica probably died of complications of old age. She was not a martyr but lived a martyr's life.
Saint Agnes of Rome was 12 or 13 years old when she was executed.
No, St. Augustine died of natural causes, probably due to old age.
Adam, the Old Testament patriarch, is not accorded the title of saint and was never canonized. The title of saint is usually reserved for followers of Christ - New Testament.
No, Saint Monica was not a martyr. She is known for her piety and devotion in the Christian faith, particularly for her prayers and influence on her son, Saint Augustine, who later became a prominent theologian and saint. Monica is recognized as a model of perseverance and faith.
We do not know. However, she was still quite young, probably in her 20s.
No, Juan Diego died of natural causes, probably due to complications old age.
Saint Patrick wasn't actually killed, latest researches say that he rather died from a various disease or from natural death.
We do not know when, where or how Luke died. Most resources say he died of natural causes (old age?) and yet ither say he died a martyr's death.
That was Jacinta Marto, one of the girls who witnessed the miracle of our Lady of Fatima. She died of sickness when she was only 10 years old.
Saint Benjamin the Deacon who died in Persia as a martyr in about the year 424. Only those who were followers of Christ are accorded the title of saint. Therefore, Old Testament personages may be in heaven but are not accorded the title of Saint.