If you are in some stay out vocation, you could go for night
classes if your superiors are fine with it. If you are not, then
maybe you could self-study (if you have time). You would be
overaged for JC by the time you ORD.
Poly has no age limit and there are so many courses in poly to
choose from (the choices were more limited many years ago), surely
there is one you are interested in? I would suggest that you study
hard for private O levels and enrol in a poly course that you like
if you can't go to JC due to age limit.