I have a natural widows peak. Can I have a hair transplant to have a more natural, straight hairline? I am a 19 year old male.

If you are considering surgery, it is best to have a consultation with a doctor in person.  Blindly wanting surgery without a proper examination without understanding the risks involved is not the way to go about it.

I encourage most men to wait until their are 30 years old before undergoing hair restoration. At 19 you do not know the future of your hair line so any surgery you do now could be a huge mistake.  It's easier and safer to simply shave the widow's peak if you want your hairline to look straighter.  Restoration of the hairline is an art. Every hairline design is unique in order to create the right curves and arches to fit each individual patient's facial shape and size.

You're much too young for any HT surgery. Take the time to understand your hairloss, the fact that it progressess over a lifetime. It's called Male Pattern Baldness (MPB).Even before you ever consider a HT, you must understand your hairloss and where it can be headed according to your own family history. If there are advanced classes of MPB on either side maternal or paternal, then it is very likely that you will be headed for the same. You need to "first" understand both the benefits and risks of HT surgery.You need to reserach what the effective hairloss meds are and how they work. No doubt at your age, you are more a candidate for a medicinal approach to your hairloss than surgery.After you have an understanding of your own hairloss, then see a reputable doctor who would first need to make a formal diagnosis of MPB and also to get you started on Propecia, etc.The worst thing you can do is to be driven by your emotions looking in a mirror at your hairline every five minutes, and thinking you will solve everything by just jumping into a HT.Take your time and wait to see  your hair loss progress in the next 5 years 
Best wishes