Is it too late to start PRP for my frontal hairline? (Photo)

Based on your photo I think you should try PRP first. You have enough hair to cover the bald spots when using PRP. Hair transplant is more of a sure thing but it may be a bit more expensive. 

Thank you for your question, This needs an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

Either PRP or Hair Transplant restoration is possible, but it will depend on your goals for your hairline. I strongly suggest meeting with a Hair Surgeon for Trichoscopy examination of your hair follicles. You may be a great candidate for PRP if your scalp presents a good amount of miniaturized hairs. PRP is beneficial for restoring growth factors and enabling cellular mechanisms that can turnover a dormant hair follicle into a viable, growing one. Best, Dr. Anil Shah