Board Thread:Questions and Answers/@comment-28067574-20190903053053/@comment-28067574-20190903124801

The reason I say that she was around during Chara’s presence is because she took the first flower that bloomed after Toriel left New Home (I explain this further in my first response to Jacky720).

So Alphys was around then, while Gerson was alive during the war. Let’s take 2000 years as the minimum time monsters have been underground. There were eight humans that fell in that time, so an average of 250 years between each human. That means that while Gerson is 2000 years old, Alphys is ~1750.

If Gerson is the equivalent of a 60-70 year old, that would proportionally make Alphys equivalent to 50-60. I find it hard to imagine someone of that age acting the way she does.