I'm 21 years old & have lost a lot of hair over the last 2 years. Am I a possible candidate for a hair transplant? (photo)

If you want options for your hair loss you need to see a doctor for an exam first. Photos cannot confirm a diagnosis and Internet doctors cannot give you a treatment plan.

Being 21 in and of itself does not disqualify you from hair transplant. However, your donor area from the photo you posted looks thin enough to catch my attention. You really need to see a local HT doctor to see if you are a candidate as your donor area may be thinning as well. Since all hair transplants depend on the donor area a thin donor may preclude you as a candidate I'm sorry to say. 

Unfortunately, you really need to consider Propecia.  You have global thinning.  Transplantation would not be a guaranteed result because of that.  Propecia may slow and possibly reverse the loss.  I know the side-effects are worrisome, but that only occurs in a small percentage of men.  Go see a hair surgeon in your area and consider the options.

Thank you for posting your photos. I understand how frustrating this could be for a young man. I do not think a transplant is the best answer for you at this point. It may seem like a quick solution to your problem, but is not the BEST solution now.  Seems to me from your pictures that you might have Diffuse Unpatterned Alopecia (DUPA) since you are showing thinning also on your lower temples. Patients with DUPA are not the best candidates for hair transplants because the transplanted hairs/follicles are also susceptible to thinning.I think you should strongly consider maximizing all the non-invasive options available until your pattern is a bit more established. You should strongly consider the use of Propecia or Finasteride after being evaluated by your doctor and ensuring you understand the risk associated with this medication. Minoxidil (Rogaine), Low level light therapy, and PRP injections to the scalp could also give you great results in this stage that you are now, and it may very well delay or eliminate the need for hair transplantation in the future. The most important thing to know is that you have HOPE and many patients like you have come a long way with the less invasive approach. Like anything in life, it does requires a large commitment from your part.Hope this was of helpful and Good Luck!

At 21 you are not a candidate for surgery. Depending on whether you have diffuse unpatterned alopecia ("DUPA") or diffuse patterned alopecia ("DPA") will determine if you might someday be a candidate or not. Some men with DUPA are never candidates for surgery.Options other than minoxidil include finasteride (which you've considered), laser and platelet rich plasma. The most important consideration by far is finasteride (Propecia). 

You pictures show early balding.  Your biggest enemy is the
progressive thinning leading to a full balding pattern. The degree of thinning that you are showing would suggest that
you should see a doctor who most likely will get Bulk Measurements of your hair
to determine the degree of the thinning that you are presently having. If the
diagnosis is early genetic which appears to be the case, then the best treatment would be the drug
finasteride which is highly effective in men of your age and may not only stop
the hair loss but possibly reverse it. I have seen some men of your age reverse this degree of balding.  Bulk Measurements of
your hair should be performed prior to starting the drug finasteride and then repeated in a year and this will show, over a one-year time frame, how effective the
treatment was. Once you know this information, then you and your doctor
need to develop a MASTER PLAN which will define what you need to do over the
years to come. Going directly to having a hair transplant without knowing where you will end up with your balding pattern at your age, would be a mistake. I have seen many men who have run out of hair completely before they can fix their balding. An alternative approach to your problem could be go on the drug finasteride, shave your head and have scalp micropigmentation done. This will give you a very manly, bold look while your hair loss pattern declairs itself (see web reference below)