I am a 21 year old looking for advise on how to approach receding hairline? (photo)

when you begin to lose hair at a younger age, the probability is greater that you will experience significant hair loss over time.  This rule is not set in stone, however, this is certainly possible.  I do not recommend a hair transplant at this point, however, you certainly would benefit from one.  What I do recommend is products to help you maintain your hair.  Propecia is one.  This product does have side affects that may not show up for years including depression.  Then there is minoxidil.  Finally, consider WNT act, a new product that promotes hair growth.  This product is plant based, stimulates the WNT pathway, and increases your density and diameter or hair mass.  You can buy WNT Act from amazon.com.  The Wnt pathway is the new way to approach and treat hair loss and no side effects are reported.  

Based on your photos and description I would not recommend Hair Transplantation at this time.Finasteride and/or Minoxidil would probably be of benefit now-I would suggest a thorough evaluation by a Dermatologist or experienced Hair Restoration surgeon to make a diagnosis and develope an appropriate treatment plan.

Most probably you have a androgenetic type hair
loss. I dont advice to use finasteride because of
possible side effects and being under
the necessity of using that chemical for almost life long to stop hair
loss.You would better planning to have an
exam at hair loss expert for hair restoration surgery when you fell
uncomfortable about hair styling or total loss of hair..Hair transplant can be an option for forehead reduction and correcting  asymmetry on your frontal hair line/forelock.I advice you have a FUE; you would get the desired hairline in just one sesssion of dense packing hair transplant.