Seems a little early to me but the other posters may be right, especially with the pent-up demand we have to expect. If you're sure you'll be making this trip at some point, I'd say go ahead and book flights, especially if the airline offers no-fee changes through 2022, as some are doing now. As for hotels, get refundable bookings because your plans and/or local conditions may change. And you might find that some hotels just don't accept bookings that far in advance. If a hotel website shows no vacancies anywhere around your time frame, see if they have vacancies 4-6 months from now. That probably tells you to wait for their booking window to open later this year -- or look for a hotel that will take your reservation now if it's otherwise OK with you.
Apart from flights and hotels, I can't imagine needing to book anything else more than a few weeks ahead. Check a good guidebook for sights you want to see that require advance booking (like various Vatican tours or the Borghese Gallery in Rome). If you'll want a car you could explore a site like Auto Europe, but you have plenty of time to nail that down. Likewise train tickets etc. Have fun planning a wonderful trip!