From reading,

IVF clinics by law have to retain the data on the sperm and egg donors that the children can access from age 18.

Similarly they don't give a donor's sperm to more than five families whether conception occurs or not.

Nothing happens at the age of 18.

Just imagine: do youths who move to a different time-zone, or due to the application of daylight-saving become adults earlier or later?

At 18 they become adults, and the issues of child support and custody disappear

Dear SM,

<<At 18 they become adults, and the issues of child support and custody disappear>>

How wonderful, then when they turn 18 they can find out about their biological father and immediately fly eastward to Hawaii where they are still 17 and claim child-support...

Would you accept financial support thus extorted from someone who gave you life as a donation?

As for custody, it's an obvious abuse to force others to live under your custody against their will, once they understand what it means and wish otherwise. I think that the law in Australia allows youth to disconnect from their parents at 16 and live independently, at least it used to be so.

Yuyutsu,

You just don't get it do you. The donors want to be free of any obligation that could possibly arise from their donation. Most want no contact ever, which is probably why the number of donors dropped by more than 50% just after the law requiring the release of information at 18.

If there are no donors, then there are no children.