There isn't an age restriction on such a switch and you would still be a 'new entrant' as per paragraph 14(d) of Appendix J of the Immigration Rules.
http://www.ukba.homeoffice.gov.uk/polic ... appendixj/
(d) Where both "new entrant" and "experienced worker" rates are stated in Tables 1 to 5, the "new entrant" rate will only apply if the applicant:
(i) is applying as a Tier 2 (General) Migrant and scores points from the Post-Study Work provisions of Appendix A,
(ii) is applying as a Tier 2 (General) Migrant and scores points from the Resident Labour Market Test provisions of Appendix A, on the basis that his Sponsor has carried out a university milkround,
(iii) is applying as a Tier 2 (Intra-Company Transfer) Migrant in the Graduate Trainee sub-category, or
(iv) was under the age of 26 on the date the application was made,
and is not applying for a grant of leave that would extend his total stay in Tier 2 and/or as a Work Permit Holder beyond 3 years and 1 month.
The "experienced worker" rate will apply in all other cases.
The reference to Post-Study work covers various routes and not just PSW, see paragraph 78B of Appendix A of the Immigration Rules.
http://www.ukba.homeoffice.gov.uk/polic ... appendixa/
(1) a Tier 1 (Post-Study Work) Migrant,
(2) a Participant in the International Graduates Scheme (or its predecessor, the Science and Engineering Graduates Scheme),
(3) a Participant in the Fresh Talent: Working in Scotland Scheme,
(4) a Tier 4 Migrant,
(5) a Student,
(6) a Student Nurse,
(7) a Student Re-Sitting an Examination,
(8) a Person Writing Up a Thesis,
(9) an Overseas Qualified Nurse or Midwife,
(10) a Postgraduate Doctor or Dentist, or
(11) a Student Union Sabbatical Officer,
