For financial reasons we waited until ds was 2 until starting again, and fell straight away so fx there will be 2 years and 9 months between them. Actually I'm glad we waited this extra year (I wanted to start around this first birthday), especially seeing how our friends are coping with age gaps of 18-24 months.
For us it was the right choice to wait, as my son gets to be the baby of the family for an extra year, hopefully he'll be happy to play a bit more independent. be willing to help mummy out with the baby, and will not be teething! Ideally I would have lost the baby weight from the first time too, but my fondness for chocolate has been too strong!
Theres no perfect age gap, pros and cons for small and large gaps!