The previous commemorative medal was awarded in 1977 before he was born. Where would he wear his award until such time as a new commemorative award was made (In this case 2002) ?
I know this is hypothetical but rules must cover ALL circumstances.
The commemorative award previous to 1977 was the coronation medal in 1953. The next one is likely to be either;
The 60th anniversaary of the QE II accession or
The coronation of Prince Charles (or Prince William if QE II lasts for a lot longer).
The next is planned for the 60th anniversary in 2012, it has been promulgated somewhere.