I didn't feel anything different when I woke up at 50 rather then 49. Of course, I forgot it was my birthday until people started calling & texting birthday wishes. Maybe I'll feel different at 51, but I doubt it. After 30, age tends to seem irrelevant.
I guess I shouldnt be on this thread because I've not reached that age as of yet. But I knew I was getting "old" when my students started calling me "sir". :D I don't like it, but there could be worse things they might call me.