Wiktionary
adultlike
a. Resembling or characteristic of an adult
Usage examples of "adultlike".
Quint stated with adultlike certainty, then walked to the front of the truck where Chase waited for them.
The boy sat as tall as he could in the saddle, his shoulders squared with adultlike importance.
His boot touched the first tread and a young voice reached out to him, adultlike in its greeting.
Cathleen informed Ty with an adultlike air and reached to take his hand and lead him up the steps to the house.