Do you think Same Sex Marriage will be legalised?

I just saw that the same sex marriage referendum will take place early next year.
I was thinking will it get passed or not. I know a good few gay people including my brother so I would be voting yes.
I was then thinking about people my age(20s) and how they might vote. A lot of them are against gay marriage and some who would be in favour of it would be to lazy to go and vote. These people now are well educated people(doctors/studied law/nurses/teachers.
Then there's also the older generation. Before my brother came out my dad would have be homophobic. When my brother came out he changed and if his friends made a homophobic comment he'd give out to them. I suppose when my brother came out being gay was normalised to my dad.
I have read that a lot of the opinion polls are in favour of same sex marriage but I'd question this happening on the day.