No, just like there is no age restriction on opiate prescription drugs. Having said that, it will be harder for you to get a recommendation if you are under the age of 18 than if you are over the age of 18 and some Doctors will want to have your parents present at the appointment. Then after you do find one then you have to find a dispensary that will work with you as most do have an age restriction for membership.
If you are legit and have a valid reason for the recommendation you will be able to get it and you will be able to find a collective you are able to join, but if you are just looking to get a license to get high with your buddies, you will run into some obstacles (not saying it is impossible or right or wrong, just what it is IMO).
I am speaking for CA state laws, other states/countries could be different.