year, new-years, person's age
秊 centers on the cycle of a year: the passing of time, the new year, and the age a person reaches each year.
秊 is an older form of 年. It combines 禾 (grain) with 千, likely representing the annual harvest cycle. The modern 年 is a simplified derivative.
The top 禾 is grain, and the bottom 千 is a thousand. Picture a thousand grains harvested each year, marking the passing of time and a person's age.
For ネン, imagine a new year starting and someone saying 'Nen' as a short, memorable sound for the year: Nen -> ネン, and the grain harvest begins again.