My son was born at 33 weeks. He is almost 10 weeks old and still hasn't smiled yet. He smiles while sleeping but no purposeful smile yet. I know I should be treating him as a "3 weeker" but he is cooing and holding his head up stronger but no smile and it makes me worried.
Re: when did LO smile?
For this - and all milestones really - make sure you look at adjusted age. My son did it somewhere between 6 and 8 weeks adjusted - which is just about when the books say it should happen.
I wouldn't worry at all - I think you still have another month or so before you should see a real smile.
My DS was a 26-weeker. he smiled at about 2 1/2 months adjuted and between 5.5-6 months actual.
Don't forget to adjust the age.