I'm 32 yrs old and low donor density. Any suggestions? (photos)

If your doctor (who has examined you in person) says you're not a good candidate for surgery, then you're probably not a good candidate.  One alternative option (which may or may not be in your particular case) would be Scalp MicroPigmentation SMP.  See some before after photos in the video.

In my opinion, your diffuse hair loss is a pattern of genetic hair loss. I don't know why you are averse to starting minoxidil or finasteride. They are probably your best choices. We have used platelet rich plasma to treat your condition. We have noticed an increase in hair thickness as well as a decrease in hair loss.  PRP will have to be continued approximately 3 times per year.Hope this helps. Good luck.

Patients with thin hair are not automatically disqualified as hair transplant patients. If that were the case there would be no HT industry. However, patients with miniaturized donor areas are disqualified. That's what it sounds like you were told by your HT doctor. But this may not be the case. You need to see one or two more experienced HT doctors for an opinion. I have plenty of patients who look as you do on the top in the photos you sent, but still have strong donor areas. We use that donor area to strengthen the hairline and frontal third area to frame the face and it works like a charm. 

Some men develop a pattern of genetic hair loss known as diffuse unpatterned alopecia or DUPA. You can read more in the link belowThe best options are minoxidil and finasteride but you can consider low level laser and platelet rich plasma. Hair transplant is not an option. These hairs miniaturize even quicker with trauma of surgery.To answer your question, no it is quite unlikely your donor area was always thin with 1s and 2s. You most likely developed this thinning in parallel to the thinning in the other regions.You are wise to be caution about side effects of any medication. But sit down first with an experienced physican to gather all the facts.

naturally thin and/or be a diffuse pattern hair loss that is common in females but occurs in males as well.  You still have potential for a transplant, but the results just wont be as amazing as a patient without this pattern.

It is best to find the cause for your hair loss and then consider the proper treatment options. If you have diffuse thinning then you are not a good candidate, but from your pictures you may have the typical male patten hair loss and could be a good candidate got hair transplant surgery. I would recommend to get another opinion from an experienced hair restoration specialist to see if you indeed have diffuse hair loss. 

This is a condition I wrote about in the 1990s called Diffuse Unpatterned Alopecia (DUPA). Assuming that you indeed have this condition, it is a contra-indication for hair transplantation.  The cause if this is unknown, but I generally put these patients on the drug finasteride and re-examine them in a year or so.