my sister is 10 years older than me and my brother 13 years older
When I was very little, it was great, as they spent loads of time with me, taught me to read/count etc. extra early, and also turned me into 'Baby Giorgio, the circus child' (i.e. tried to make me do 'tricks').
then there was a period when I was obviously a pain in the arse to my sister, when she was about 17/18 onwards, and long periods where they were both at university and so it was like being an only child for me for quite a while. My parents used to travel a bit for my dad's work and often my sister and brother would look after me; they came to a few parents' evenings (the shame) and were there to see me get my scholarship when my parents were away. So sometimes it's been a bit difficult getting them to see me as a sibling rather than as a child, and getting seen as 'equal'
However, in many ways that was very good for me. I had to learn how to hold my own in an 'adult' conversation pretty early on, and how to fit in with older people and not appear childish, and how to argue!
I don't think I've missed out. There's no guarantee as to how well you get on with your siblings whatever the age gap is. I feel like I've had an insight into what it's like to be an only child as well. I get on very well with them now and although I'm still very much the little sister I think they've accepted me as a grown up now I'm 33 with 2 children...seriously, the age gap seems so much smaller now that we're all proper grown ups. Obviously, it was huge when I was say 8 and they were 18 and 21, but it all sorts itself out.