I think you really need to discuss things properly with your fiancé (forget everyone else, it's not up to them!!)
Does he have any particular reason why it needs to be then? (Other than the "why wait" aspect).
Personally, purely from an organisational point of view I would have found 9 months to be too soon - but then again I am not a particularly organised person and I have found wedding planning to be enormously stressful, so other people may have a completely different view. You start off thinking 9 months is ages, but it's actually not, you have to get onto booking both venues (church and reception) right now pretty much - since June is a popular month, so venues will start getting booked up quickly - after agreeing on a rough guest list, so you have an idea of numbers, then finalise your guest list (this can get pretty fraught, although not always) so you can send out save the dates or whatever in the new year, before people start booking their summer holidays. Then there is just so much that goes into wedding planning that I would never have even thought of. We've had about 13 months between engagement and wedding and I feel like we've needed all that time. But as I said, maybe that's just us, some people absolutely love the planning aspect and would be fine with 9 months or even less. Also if the people who are pressuring you into having a June wedding are willing to take on some of the work of planning, maybe that could be a good compromise?! But if all the planning is going to fall on you, you really should be able to say "no, it's not enough time".
Are you all dead set on a summer wedding, or would it be OK to wait for the autumn, which could be a good compromise, giving you a bit more time whilst not having to wait a whole extra year..? (Plus the venues and suppliers will be less in demand..)
Or is it the emotional aspect that's bothering you - i.e. you don't feel ready emotionally to get married so soon? If that's the case then I think you really need to talk to your fiancé and find a way of explaining that you really need more time. It's really not a good idea to get married if you don't feel ready, that's a recipe for disaster and your fiancé should be able to understand that if you explain. It doesn't necessarily mean you're having second thoughts about marriage, I could just be that you need time to get your head around such a momentous change, which is totally normal, and you want to go into it feeling 100% ready.