You can always start planning whenever, but I wouldn't book anything until within 2 years of the wedding date. Before then, getting inspiration on Pinterest, researching, and looking up ideas online is always a good plan!
When are you getting married? It’s never too soon to start looking at ideas & inspiration. I would suggest creating a Pinterest board with things you see that you like. That’s what I did and it was very helpful when I shared it with my wedding planner. Best wishes to you!