How do I prevent a receding hairline from getting any worse?

You generally cannot "stop" genetic hair loss.  There are medical and surgical treatment options but these are not "cures".  You first need to see a doctor for an exam and establish a treatment plan.

If you have thinning hair you really need an evaluation to see if it is genetic or from another cause like stress or autoimmune. If it is determined to be genetic there are many options and traditional treatments like rogaine foam and propecia pills can be used. I have great success in my practice using injectable progesterone and prp to the scalp. Viviscal is a must as an oral supplement.  Postmenopausal women also benefit from spironolactone. I suggest seeing a dermatologist with expertise in hair loss. Best, Dr. Emer.

In my opinion, Minoxidil is better for the crown. Finasteride and low level laser have been report to improve hairline and crown.PRP works well if you have not lost a lot of hair in all locations.It's important to see a hair specialist who can take a good history, blood tests, examination  and possibly  biopsy.A combination of modalities probably will work best as will starting at an early age.Good luck!

Hair loss at the age of 17 years can be due to hormonal ( Androgenetic Alopecia) or dietary issues as well. It is better to start to visit a hair specialist doctor to evaluate the kind of hair loss. Without seeing your pictures, it is difficult to comment however, in general the treatment protocol for hair loss in young males will include: Finesteride, Minoxidil, multivitamins and Platelet rich therapy.

The use of Propecia is mainly for protection of  the crown area. You can try the use of Minoxidil 5% to see if it helps slow down the hair loss. Remember that in the end it is a genetic process and if you have balding men/women in your family then most likely you will receed more over the next years.

In general terms, the first thing for anyone with hairline changes to determine is whether they have hairline maturation or balding. A hair specialist may be needed to help sort that out. There are no treatments for hairline maturation. Treatments for male balding related recession at age 17 include:finasterideminoxidillow level laserplatelet rich plasma