the tradition is that Mary was 15 when the Angel Gabriel visited her, 16 when Jesus was born, so 48 when he was crucified (her birthday being Sep 8th)
The brothers of Jesus or the adelphoi (Greek: ἀδελφοί, translit. adelphoí, lit. "of the same womb") are named in the New Testament as
James, Joses (a form of Joseph), Simon, Jude, and unnamed sisters are mentioned in Mark and Matthew.
(1) Luke says Jesus "opened the womb" (and Matthew confirms that Mary's pregnancy was a surprise to Joseph and he thought she was sleeping around before they were married), so it seems Jesus was their first child, even though "Joses" was named after his father and that is usually what happens with the first child.
(2) James is attested both in Paul and Acts as "the brother of the Lord" and a leader of the early Church. His killing is also mentioned in Josephus, and the then high priest is removed by the new governor for acting outside the protocols by killing "James the Just" while the new governor was enroute to assume his position after the death of his predecessor.
(3) Luke (only) has the story of the "boy Jesus in the Temple" wowing the scribes with his knowledge. He is supposed to be 12 then, and since there are at least 6 other kids some at least must have been around then. That means that if Luke is accurate (of course not--it's Luke) the parents traveled to Jerusalem with little kids in a big caravan (for safety) and left them with the caravan to go back and search for the missing Jesus.
Given all this, I think "tradition" is mostly urban legend, and Luke is just making a lot of stuff up (like the "cousin of John the Baptist" story--in an effort to date Jesus, people have looked for a priest named Zecariah, John's supposed father, in independent sources and come up empty). Matthew's and Luke's nativity stories and their geneologies completely incompatible as well, and John says flat out that Jesus was not born in Bethlehem.
(Maybe the Hollywood writers were on strike then, too, and scripts got garbled.)