PG Cert in Psychology

1) As far as I am concerned, HKU is better because of two reasons. Firstly, the department has a longer history. It has developed a very strong psychology research basis. Secondly, the schedule is less tight so that you can assimilate knowledge better. Actually, the workload of studying CU is much heavier than that of studying HKU. You are likely to have a very tough school life if you study CU.
2) You are eligible for applying master degree in psychology (Clinical, Educational, Industrial and Organization or Research) after you get the postragduate cert/diploma in psychology.
3) 10 persons per year in 2004 when my friend study the course.
4) Normally, the mean age of PgCert/PgDip Psychology around is 25-28. So it is unlikely that you will be a lot older than other classmates.
5) I do not think that your qualification is a problem because it is pretty competitive. However, I would recommend you to think about your motivation. You have to do some research on what you really want to do (e.g. Clinical psychologists? Psychology researchers?)
Additional point: The course is really an interesting one. However, if you consider it the cornerstone of your future career, you really have to do some career research and think twice before you take the course.