Board Thread:General Discussion/@comment-27324545-20160105135410/@comment-31196611-20170505202624

For me I'd say:

Frisk 8 -12

Chara 9 -12

Toriel / Asgore Almost a thousand if they were in the war.

Papyrus 18 - early 20s

Sans, Undyne, Alphys - somewhere in the early to mid twenties

Asriel 7 - 12 (Older counting his time as Flowey)