why is my name bold, size in large and coloured red? 
anyway. it's not that complicated at all. not getting enlistment
letter by age 18 is not something unusual. many people get called
up at age 19, 20, 21 or older (for various reasons like studying
etc)
in this case, i'll strongly suggest TS to call up ICA, make
arrangements, take a trip down to asap and do the application for
your IC. this whole proces till recieving the actual IC will take
months so do it quick.