At what age should one start to TopUp their CPF SA to reach FRS? Is it adviseable to TopUp CPF Special Account at young age?

If you have the means, why not start early! At least one goal achieved.

Right when you receive your first pay cheque when you don't have so many financial commitments, seriously. Like what another user said, there seems to be a growing trend of savvy and determined Singaporeans who hit the FRS in their EARLY 30s. In addition to have $100k portfolio if you are feeling really competitive, haha.

anyway, I don't feel FOMO but I attained FRS when I was 40 - and felt that I was just desperately trying to make up for lost time. Don't be like me!

I would recommend topping up CPF SA when your assessible income exceeds 80K as this would provide you with a good amount of tax relief.

I would actually recommend topping up your CPF MA first to BHS, then consider topping up to CPF SA. This is because CPF shielding does not apply to voluntary contributions to SA.