hmm.. can only speak from personal experience...

My bro is 5 yrs older than me. As kids.. it was nothing but tormenting me. When I was mid-late teens we hung out together quite well. I didn't expect to go out with his friends or anything (mainly coz they were over 18 and were out at bands and pubs & stuff) but we got on well and hung out at home together. As adults we've drifted apart but nothing to do with age.

My kids are 19mths apart. I can totally see how a big age gap would be easier parenting wise LOL. But they do play together and I *hope* they grow out of the current rivalry. I'm thinking perhaps it's just a big brother thing... they're all mean to their little sisters! LOL.

I'm sure you'll get whatever age gap you end up with to work