I think Eclipsa would be 19 because throughout the show,she would get teenage tendencies.Her face is also still round,not childish round,just teenage round,like Star's.I know 19 would be really young to have a lover and give birth to a baby,but Eclipsa tells Moon in the episode,"Moon the Undaunted",that she lost Solaria when she was not much older then Moon.According to the Star Vs the Forces of Evil:The Magic Book of Spells,Moon lost her mother,Comet,when she was barely 17,so I was thinking that Eclipsa would be 19 .Also,we have to keep this in mind:
1.This is medieval times we're talking about
2.Disney made Eclipsa old enough to have hot monster...well...let's say they made her old enough to get it on with a monster
3.Eclipsa was married to Shastacan right after Solaria died,so if she wasn't much older then Moon,then she was probably 18
4.Eclipsa had teenage tendencies throughout the show
5.Eclipsa still has a teenage-round,but more adult-looking face then Star's
6.She is definitely younger then Moon
