Understanding Society User Support

Hi, I need some advice on analyzing a subpopulation of the sample. Specifically I am only analyzing individuals that were aged 16-24 in the first wave and who have a 'full interview' at each subsequent wave.

Previously I had been just been applying a filter to the data and still using the sample weights, but it has occurred to me that this might not be statistically sound thing to do. What do I need to do in order to analyze this subpopulation correctly using spss? Also, would I need to adjust the sample weights manually at some point?

Thanks,
Stef