Deep cleaning for a 15 year old?

So I just went to a new dentist today, and she looked at my teeth for a little and said I needed deep cleaning. I'm only 15! I brush my teeth twice a day (morning and night) but I'll admit I don't floss. I know even some kids at my age don't brush at all sometimes and they probably still wouldn't need deep cleaning! I've never had deep cleaning before and I haven't changed the way I brush except I brush even better now. What is deep cleaning? Is it even right for a 15 year old? My new dentist runs on 5 reviews all with 1 star on Yelp, should I trust what they are saying?

[feelinglost824]

I have seen teenagers that have needed a deep cleaning.  And for different reasons.
Some have poor oral hygiene habits, some for other reasons like medications, genetics, etc.  
Deep cleanings are indicated when peridontal disease is evident.  There are several stages of severity of periodontal disease.  The periodontal cleanings are necessary because it is impossible for you to clean as deeply as needed once periodontal disease starts.
Without knowing more about your case, it's not possible for me to know if you need it or not.  Did she do a periodonal charting?  Did she indicate how severe your periodontal problems are?  
If you and your parents weren't given enough information to understand her recommended treatment, you have the right to ask for clarity.  And by all means, if you don't get it, a second opinion is a good option.
I would recommend you to start flossing regardless of what your periodontal condition is, either to help your condition or prevent one in the future.
I hope this helps you.
Sincerely,
Chrisyt