Babies grow fast, so there can be a fairly large difference between twelve months and fourteen months, or fourteen months and eighteen months. You can't express

Babies grow fast, so there can be a fairly large difference between twelve months and fourteen months, or fourteen months and eighteen months. You can't express those values well in decimal format, so you can't discuss milestones and development in decimal format. My experience is that people usually switch over to years once the child is older than two.