I have no idea how they came up with that theory, do they have any scripture to support that idea?
It's already been covered - see the Protoevangelion of John. It's apocryphal, but one of the few places they are referenced.
On another note -
The whole thing with Joseph is kind of interesting – there are several schools of thought depending on which branch of Christianity you adhere to.
The general belief is that he was older than Mary. Indeed, in Christian iconography, particularly Eastern Orthodox, he is typically depicted as an old man. Oftentimes, even in Western art, it looks as if he’s almost staring off into space and is totally removed from what’s going on around him. This was explained to me as being done purposefully to detract attention from Joseph and focus it on Jesus. Joseph is there, but is sort of 'artistically faded' into the background, so to speak.
If Joseph was in fact older and a widower, commonly the reasoning behind explaining Jesus’ brothers and sisters mentioned in the Bible, Jesus had step-siblings. And Mary had step children who may have even been older than she was.
This is, I believe, the Eastern Orthodox view; i.e. that Joseph was older and a widower with children.
I’m not sure I agree with this theory though. Let’s face it; an older man with several older children in tow hardly makes for an ideal marriage prospect for a young girl of marital age.
In Western Christianity, he is generally older, possibly a widower and possibly with other children. Not all agree as to whether or not he was a widower, and if so, whether or not he also had children from his previous marriage.
I don’t think Joseph was all that much older than Mary. If Mary was around 15-16, Joseph was most likely around 18-20. Children named as brothers and sisters of Jesus were his actual siblings; all born after he was. This view, of which I’m not alone in thinking it, is regarded as sort of ‘heretical’ in some circles, but I think it makes the most sense.
So why, by the time Jesus starts his public ministry, is Joseph nowhere to be found?
The usual answer is that he was deceased (given that he was an older man to begin with). Not sure I agree with that.
In simple terms, I think it can be agreed upon that the gospel of Mark (and the so-called Q-Gospel from which it came) as well as Matthew and Luke (who most likely copied from Mark) all essentially tell a story. There is very convincing evidence that that the writer of Mark used a particular ‘literary template’ in writing it, but that’s a topic for another day.
In the telling of this story, it’s possible we see a typical, what has come to be known as a, “Märchen-formula” being used. ‘Märchen’ is German for ‘folk-tale’ where this formula is very common and in some cases, almost a requirement for the tale.
In this formula, the ‘hero’ of the story starts off as an infant/youth and comes into his own as the main figure, i.e. the ‘hero’ of the story. When he does so, the other leading male figure (almost always the father) is simply written out of the narrative resulting in the focus being placed solely on the story’s hero. Usually the father figure is killed off or meets some other untimely demise, but the point is, when the hero comes into his own, the father figure is never mentioned again; he simply just vanishes completely from the narrative. It should be noted that in the Märchen-formula, it doesn’t always have to be the father; it can be the mother or even both parents.
This may be the case here as well – Joseph figures into the infancy and youth of Jesus, but as soon as Jesus becomes officially an adult (in this case, the temple scene when Mary and Joseph ‘loose’ Jesus and find him in the temple later – if memory serves me, he was about the age of what would have been his bar-mitzvah), Joseph is no longer mentioned in the Gospel narrative; he simply disappears never to he heard from again. The focus is now on the ‘hero’, Jesus, as he begins his public ministry.
So, in short, I personally do not see Joseph as being much older than Mary and I don’t think he died somewhere between the time Jesus was 12-13 and the start of his public ministry at about 30; Assuming he was about 20 when Jesus was born, he would have been somewhere around 55-ish at the time of the crucifixion. I think his ‘job’ in the Gospel story was done, so to speak, and he was simply edited out of the narrative. To place him back in later on would have been somewhat awkward for both the author and the story itself.