No 18 year old is going to have a degree in engineering though. And if they did, they probably weren't thinking about airlines to begin with.
Out of curiosity, the RSAF sounds like the airforce so it's okay to assume that the 26 age limit is only for SIA applicants? What about applicants applying for Hong Kong and such?
I think it's 25.5 now, and yes it's for singaporeans only. M'sians don't have this, so i don't think if applicants from HK will have it either.