I think you definitely shouldn't rush into any decisions, however, if you're very sure that you want to transition and you'll be miserable without it, then time is not a reason to wait. I recognized I was trans about 3 years before I started hormones, and the single reason I waited that long was because my parents wouldn't let me so I had to wait for my 18th birthday. If I had picked when to start, I probably would have started a year or a year and a half after realising I was trans. If your only reason or doubt about starting is that other people waited longer, I think you can relax. It can always be helpful to talk to a therapist about doubts, but I assure you that a year and a half is perfectly reasonable. If you know transitioning is what you want, don't wait just because you are comparing yourself to others' waiting. If you know it's what you want, go for it, but if you're unsure, then talk it through with a therapist.