How many circles of friends have you got (that you see at least semi-regularly, not facebook 'friends')? Personally, i've got loads. Friends from school; friends from university; friends from the 'music scene'; hell, even friends from the internet.
Also, when you talk about 'your friends', who in your mind are you referring to? For me, it's my circle of school friends. I guess just because these are the people i've been friends with for longest. Even when we all went our seperate ways for uni and made new friends, we all just seemed to gravitate back towards eachother after graduation.
Like the author i'm nearly 30, but I haven't seen any marked change in my ability to make new friends. Sure, it's easier at places like uni, but I still seem to pick new friends up from time to time. Not being a bedwetting virgin usually helps. Maybe the author's just a bit of a loser.