Family History continues

Well today is a new day, off to the National Library of Australia i go, still searching for my elusive ancestors.
David and Catherine Mehegan CROWLEY where did you go?
A perplexing question about my ancestor James David CROWLEY  1.  why would he lie about his age and date of birth on all his official papers, e.g. emigration, marriage and death certificates.  2.  Was he running from something or away from someone???
Hmmmmmmmmmm....sounds very suspicious to me.
So i still have no idea about my irish heritage, is James David Crowley even his real name, i am beginning to think he is a total FRAUD.  Why is he listed on church records with a birthdate of 1837 with parents David Crowley and Catherine Mehegan.
I know i am missing something vital here but i cannot put my finger on it.

Did people emigrating to Australia have to have any identification papers?

When he married in 1873 in Victoria, Australia, did he have to produce any documentation to prove who he was?

JUST QUESTIONS MORE QUESTIONS and MORE QUESTIONS.

I really feel like giving up, but now i am driven to find out who this person
really is.

His whole life has been a secret, nobody in his family or relatives knew what happened
to him after he deserted his family in 1889 - a wife and 7 children.
On his death certificate he said he had no family just Mother: Catherine Mehegan and Father:  David Crowley.
It was only recently (quite by accident) that one of my relatives found out he was buried in Corowa NSW.  For years his grandchildren used to relay all sorts of different stories about where he went, but in the end, he only moved a little way away from where he was, when he was married.

Most of the Crowley's who emigrated from County Cork, Ireland seemed to have lead successful and productive lives, James David's occupation when he came to australia was a Labourer and when he died his occupation was still Labourer.  All in All a very sad life i should think.

Well i am off for now!!! Going to a little seminar on Looking Up Passenger Lists tomorrow, hopefully i can ask some questions that might help me.