It's unclear when this competition began. The earliest mention I've found of it was in a 1976 copy of the “School Mathematics Journal” of the Newcastle Mathematical Association. It is not described as being a new competition, so while the competition did run in 1976, it probably existed earlier than that.
The name appears inconsistently. Sometimes it appears as Colin Doyle Competition, sometimes as the Colin Doyle Mathematics (or Maths) Competition. In its earlier years the documentation uses some verbal gymnastics to avoid referring to the competition by name, and instead it refers to the contest as being to determine the winner of the Colin Doyle Memorial Prize. (Yes - there was only one prize. Apparently there are now prizes for the top 3 students.)
Initially the contest was available to Year 11 students in the Hunter Valley region of New South Wales, Australia, but more recently it has expanded to also include the neighbouring Central Coast region.
The MANSW web site has some recent competition papers and solutions. Older papers are harder to find.
I had a copy of the 1980 paper handy. It has some interesting question, so it would be a pity if it disappears. The exam paper distributed to entrants carries no copyright notice. I believe this places it in the public domain. So here it is.
Note that while the competition was restricted to Year 11 students, many of the questions are accessible to junior high school students. Q1(c) and Q4(b) might even be accessible to primary school students.
Here's some partial solutions. I started with the harder questions. If I find some spare time, I might also write some solutions for the routine questions.
If anyone reading this has access to other exam papers from this vintage, I'd be interested in discussing whether they can also be "salvaged" if they are in the public domain.