I put 3+ years and I think we'll aim for this baby being 3 yrs old when next one is born ish.
I originally after having my son wanted a second when he was two ish but things didn't work out quite that way. And it's been so nice for my son to be able to understand whats going on, admitedly he's four and a half but I think at three he wld of be fine too. Besides I don't really want any children when I'm over thirty four, lol!
However I will say all my mates who had children around same time as me, well within a year all got broody when baby hit nine months, including me! LOL So who knows maybe it'll be earlier?