I think it is more about life experience, which happens as you age of course, rather than age itself. I am a laid back person most of the time. I don't know if it is that I expect less of people now than I did when I was younger or if I have simply given up and now just assume everyone is stupid and/or self-centered until proven otherwise. I know that sounds funny, mean and/or cynical to say, but I am actually being serious about that.
For me personally, it's the lack of respect and consideration people show for one another these days that bothers me the most. I don't care if people are nice to me as my expectations are lower, but it bothers me when I see people being mean to others, especially when there's no reason for it.