A young nation or not, it shouldn't affect make us -- true blue Singaporean -- any lesser Singaporean than we should be.
Our past generations(parents and grandparents) had their shares of their trials and tribulations. While we, the younger ones, also had the unique experiences of growing up in a multi-racial society, competing in our life's first few rat races(PSLE, GCE), living in our clean and safe HDBs and doing NS when coming of age. All these helped formed the main cores of our Singaporean identity of today.
The challenge is how to integrate the "new" Singaporeans -- make them feel more like "Singaporean" -- who took up the citizenships during the recent years, when immigration policies had been lax.
But I'm afraid it would be a improbable task though; it is extremely difficult to "uproot" the emotions and feelings that were attached to the place of your birth, and faithfully swear allegiance to a foreign place. And I reckon that the true integration only starts with their offsprings.