Is it normal to feel depressed when I look at pictures of weddings/baby showers/ parties?

I'm in my late teens and not married. It's not that I'm jealous, it's kind of the opposite. Maybe it could be that I might not want to get married or have kids. It seems like people are just "going through the motions" to me. Even pictures I'm in of these things depress me. When I go things like baby showers or weddings, I'm happy for the people getting married but sad that it might end up being me one day. Maybe it's just that I don't really know that many people happily married (that aren't newlyweds). Is this normal?