question about joining

[jgunn77]

hello,
i'm a 29y\o and i'm at a point in my life where i have a burning desire to join the army and help defend my country....my question is this:
1)how common is it for someone my age to join

2)if i join at this age, would i ever have a shot at SF or Rangers or is there an age limit and how long do you have to be enlisted before you could possibly start SF training if you meet the qualifications...

thanks for your help