Years and months; the passage of time over months and years. Can refer to a long period or the time span measured in years and months.
年月が経つと、その建物もだんだん古くなった。
As the years went by, that building gradually became old.
年月をかけて研究を続けた結果、大きな成果が出た。
After years and months of research, great results were achieved.
年月を感じさせる古い写真を見つけた。
I found an old photo that shows the passage of time.