I'm also using a travel agent but even though flight prices/times aren't out, we were still able to book our hotels and flights together. We have over 40 people who've booked so far. We sent out our save-the-dates as soon as we picked out the resort (around November), so I don't think it's too early to send out save-the-dates. It just gives your guests more time to save up their money and gives you a better idea of how many guests will come. I never thought that many people would book so far in advance, but people surprise you.