I've read two schools of thought on this:
The first is that, if someone has not had very many children, it may be better to have children closer together rather than years and years apart due to not having to re-stretch all the tissue to the same extent.
The second is that, if someone has had a lot of children, it may put more strain on their body with a greater risk of incompetent cirvix, miscarriage and eclampsia, but still doable.
My husband and his sister are (bless their mom's heart!) eleven months apart. Someone resumed regular activities before they were supposed to!