The age to be mentioned in the application form is the age of the applicant at the time of application (extension application, in this case) and not the age of the applicant when an initial application for HSMP approval / Tier 1 (General) / EC application was made 2-years ago. In April 2011, you'll be 33 (Read para 69,71,73 of the policy guidance).
This said, as per
this post of yours, you switched to student visa in Sep 2009 and are now in UK as a Tier 1 (PSW) migrant. So how does the question of HSMP extension arise?
No offence but before you "dictate" that people suggest/answer only if they are 100% sure, you should be honest about your own status in the UK! No point in beating around the bush when UK immigration rules may not allow what you intend to do (e.g. - apply for HSMP extension when on Tier 1 PSW)!
regards