ikäisiinsä

The Finnish word "ikäisiinsä" is a grammatical form derived from the word "ikäinen," meaning "age" or "of age." Specifically, it is the illative plural of the word "ikäinen." The illative case in Finnish indicates movement into or within a place, state, or category. Therefore, "ikäisiinsä" literally translates to "into their ages" or "among their ages."

In common usage, "ikäisiinsä" often functions adverbially, signifying a comparison or grouping based on age. It is frequently used in phrases that suggest someone is behaving or has developed in a way typical for their age group. For instance, one might say a child is "acting their age" or "developing as expected for their age." The form implies a natural progression or a fitting within the established norms of a particular age bracket. It can also be used to describe individuals who are similar in age to one another, forming a peer group. The context of the sentence will clarify whether it refers to a literal movement into a group of people of the same age or a more figurative sense of belonging or fitting in with one's age cohort.