Babiest
A superlative adjective used to describe the extent of babiness in a high functioning adult with huge achievements and ambitions that also, exhibits baby like tendencies, like throwing tantrums, loves shiny new things, goes on baby strolls, listens to music in order to calm down and loves constant attention. So when the baby tendencies flare up, it is safe to use the adjective and compare it with a literal actual baby.
My fiancé has constantly proven that she is the babiest baby in the entire world by constantly saying and doing baby things for almost 3 years.