Incorrect. This is a common misconception. It is not relative to age if he is diagnosed with primary or secondary hypogonadism, which unfortunately is a distinct possibility.
Get a full blood test workup. Tell the Dr. you want everything tested. The important values that could shed some more light on this situation are the ones that follow. The widely accepted normal values are in parentheses. Please keep in mind that some of these "normals" vary from lab to lab, but they are all relatively in the same ball park so to speak.
Testosterone Serum: (usually 300-950 ng/dL)
Free Testosterone: (9.3-26.5 pg/mL)
Luteinizing Hormone (LH) = (1.5-9.3 mIU/ml)
Follicle Stimulating Hormone (FSH) = (1.4-18.1 mIU/ml)
Estradiol (estrogen): should
preferably be less than 30 for us bodybuilders (0-53 pg/ml)
Sex Hormone Binding Globulin: (13-71 nmol/L)
Prostate-Specific Antigen (PSA): Might as well get this one while you're at it, never too early to check (0.0-4.0 ng/mL)
Thyroid Stimulating Hormone (TSH): (0.450-4.500 uIU/mL)
Thyroxine (T4): (4.5-12.0 ug/dL)
Triiodothyronine (T3): (2.3-4.2 pg/mL)
T3 Uptake: (24-39%)
Also be sure that your blood is taken in the MORNING! Make sure that you get plenty of sleep and rest for the 3-4 days before your blood is taken. Also try to minimize your stress levels during this time. Eat a healthy diet, with plenty of healthy fats and stay well hydrated.
I would not hang my hat on one blood test. Especially at your age. I would however do some research on all of these aspects of your blood tests, and what these hormones do physiologically. A thorough understanding of your endocrine system can go a long way into figuring out what these numbers mean, and how they relate to your health. This will ensure that you can interpret these values YOURSELF! It is YOUR body and it is YOUR life so it is YOUR responsibility to educate yourself so that you never have to take another persons word on what is best for you and/or your condition. Many good bros on here can testify to the fact that there are NOT that many doctors who are properly educated on this particular topic.
As far as over the counter supplements helping with this, forget about it. I know you want high test levels so you can get bigger muscles, but you need to find out what the hell is going on with your endocrine system, because a test level that low at your age is quite abnormal. You should find the problem before you try to treat the symptoms. I hope this helps, and good luck brother.