usually they are eleven months apart or born in the same month one year apart as your body needs time to heal before you resume intercourse after delivery and because of risk of miscarriage if your body hasn't healed
Irish twins are babies born within one calendar year of each other. I was going to, but miscarried. I did get pregnant a couple months later, so my two are fourteen months apart and it's difficult more in the toddler years than in the beginning, but mine are only one and two so that's all the experience I can give you!
Its hard as hell, but pure joy!