Sounds terrible, and yes, you are very young to have this pain, but whether or not you should have pain is not the issue.
Innervation of the legs comes right through the lumbar spine, so your leg pain could very well be from lumbar stenosis, however, just seeing L5 stenosis on an MRI does not provide enough information to diagnose your problem. Many more questions must be answered. For instance, is your stenosis mild, moderate, or severe? Do you have pain in your groin, buttocks, lower back, or in the upper part of the leg? How are your peripheral reflexes? Have you had any nerve conduction tests? Etc. Etc.
It is unfortunate that most primary doctors in the US don't know what to do with back pain, and usually their first response is to refer you to a surgeon. While I understand why this is done (safety -- you don't want to end up with paralysis), surgical treatment of pain should be the very last resort, not a first option, unless there is a medical emergency. Some back conditions can cause paralysis, but most patients present with less exotic forms of back disease.
There are some excellent spine doctors around in multiple disciplines, however, you have to know what to look for to find the right doctor.
There are excellent pain management programs at some of the university teaching hospitals around the country. I'm a patient at the University of Colorado Pain Management program, where I have access to a variety of treatment options, but looking at their website, you'd have a hard time understanding why they have a good pain clinic.
I usually recommend interventional pain management physicians to back patients here because their training is in non-invasive, non-surgical techniques for reducing pain. These doctors hold a wide variety of specialties -- anesthesiology, neurology, orthopaedics, sports medicine, and others -- but all have advanced training in the spine and interventional pain management treatments. See this page for more info:
There are excellent surgeons who also have this training. Dr. Wm. Dillin in Southern California is a good example. Dr. Dillin is a trained surgeon, but also has trining in interventional techniques. This is rare, because surgeons can make three or four times the amount of money doing surgery rather than doing an epidural steroid injection, so many have the attitude of why waste time giving injections when I can make real money with a scalpel.
Dr. Dillin has an excellent, informative website all about spine conditions and treatments. Take a good look -- there's a world of medical information in here: http://www.spineinformation.com/about-dr-dillin.html
These sites will help you develop the knowledge you need to find an answer to your problem. Educated yourself, and find a trained pain specialist to help you understand and treat that leg pain.
It can be from your back! I have severe back problems ( herniated disk, nerve damage, spinal stenosis, tethered spinal cord just to name a few) I started having pain in my leg. It felt as if my leg was being crushed! I ended up in the er where they did a x ray and found nothing, I went to my GP and he ordered a ct scan still nothing! He then asked me to stand put all my weight on my good leg. He pressed a spot on my hip and I almost fell. He dx me with bursitis gave me a cortisone shot and I walked out of his office. ( I went in sitting in a wheelchair) I started having the same problems recently and the shots were doing no good! So frustrated. I went to a naturopath chiro because I was having back pain. They do NOT twist you and force the back in!!! One side was 3" shorter than the other. He said no wonder I was in pain. That it was causing all of my muscles from my neck to my foot to pull. I am now doing therapy with him to get my muscles to stay where they are supposed to be and feel a lot better. My hip pain is going away as well as the muscle pain. I do not know if this is the answer for you but it would be worth checking out. Also if your spine is degenerated you probably have a lot of inflammation. I take NOW brand black cherry capsules and they help more than any script I have been given. If you need any more info feel free to message me :) I hope you are better soon. Best wishes, Sissie