Two of my permanent teeth never grew (lower second premolars). i am 17 years old. is that normal? can you live just as well without those?

More than one answer: First, "Is it normal?" It's uncommon but not abnormal. Second, if you haven't had any problems so far, you should be able to live well without them. Not being privy to you dental x-rays, I don't know if the teeth are there but haven't erupted and I don't know if you have 3rd molars (wisdom teeth) Based on x-rays, your dentist can predict if you might need dental work in the future.

"Never grew": Do you mean they never formed, or they never erupted (they are impacted in your jawbone)? It is not out of the ordinary, and is usually hereditary. You'll have to live without them since you don't have them... the question is if there is a space there and how does it affect your occlusion? The answers to those questions can be found during a consultation with an orthodontist. Make the call...