I'm the same age as you. Are you in college/school? If you're not then you have to understand that everybody's busy doing their own thing. Most of my friends have gone off to University (as I'm a uni drop out, I'm back at home).
Besides, most of the people you know around the age of 19 are only temporary. You'll meet a lot more people later in your life, so just have that to look forwards to.
I don't think there's any age at all where you "find your true friends"
I haven't maintained friendship with anybody from education, employment or anything 'forced' like that, with friendships very quickly dissolving after leaving each thing. You 'have to' be friends with people in these situations rather than 'choosing' to be friends with people and letting a friendship develop naturally. You're 'friends' with them because it's convenient since you're going to be stuck with them for the foreseeable future.
It's not how I think about it at the time but when I look back at old friends from these places, it's not hard for me to see that we just wouldn't have been friends outside of 'the place'.
On the other hand I have been friends with my 2 best friends for 8 and 5 years, and I met neither of them whilst in education or work.