Alexandra,
Firstly let me say I think you are terrific for even thinking about donating. What a generous gift. I have had an egg donor and i can tell you about my and her experience. She was not a good friend she was just a girl i met through someone else and like you she had 3 beautiful children. Firstly they don't usually take eggs unless you have completed your family. There is no expense to you just a little discomfort. You have no legal obligation to the child. The eggs are yours until they are taken from you - ie my donor was told she could back out at any time even if she was on the table about to have them retrieved she could back out - after the eggs are removed they now belong the other woman. You will have to do conselling to make sure you understand exactly what you are doing. No you are not too old at 35 i believe that if you are under 38 its ok.
They will need to run blood tests first to make sure that all is okay health wise. I don't know about victoria so that something maybe someone else can answer but maybe just contact Melb IVF and do some enquiries and i can tell you you will be a very popular girl.
You will most likely have to do something that is called a memorandum of understanding between yourself and the parents to be - eg: its not a contract its just and understanding - for example when we did ours there is a strong preference with Sydney IVF that the donor has some sort of part in the childs life if possible. They beleive as i do that the child has the right to know exactly where they have come from and they suggest you start telling them when they are just babies so you are comfortable telling them the story and they just grow up with it and its not a huge shock at 13yrs of age. They even have story books now for just this purpose - its a fairytale story of how the child came to be and the books are just lovely. Anyway hope this has helped a bit - sorry for the long post. And again I for one think you are terrific. Good on you for helping someone have the chance of being a mum.