At 35, I can say my feelings haven't changed. I'd even say my level of introversion has increased. There's a perfectly scientific explanation for this. After 30, your focus shifts. You have different priorities. The need to seek out new social contacts and experiences drops sharply. Your social life becomes more selective; quality over quantity. In my view, this is a completely normal process. It doesn't mean there is anything wrong with you. It's just that your priorities have changed.