With the new release chapter 145, most of the goddesses is either founded or reveal to us (reader). Now here the pondering question which goddess is the oldest and which one is the youngest? Because they all seem to wants some “LOVE” from Keima, the one that been found, of course, an example of older have more say would be in ch137. So which Sister do you think is the oldest and which is the Youngest and who do you think will, among the goddess, have the higher chance of winning/control Keima? 3v6c1x

Well, in chapter 118, the Jupiter Sisters are introduced as follows*:
Vulcan
Apollo
Diana
Minerva
Mars
Mercury

Diana calls Vulcan 'nee-sama', so we know that Vulcan is older than Diana. Diana also calls Apollo 'nee-sama', so we know that Apollo is older than Diana. Vulcan does not call Apollo 'nee-sama', so if we imagine that they usually do, then Vulcan is older than Apollo.
I'll check and see if I can find out:
how Mars refers to Diana, and
how Mars refers to Apollo, and
how Mars refers to Vulcan,
but so far it looks like the above* order is the order of their births/ages.

Also, Keima's heading for a harem ending, no doubt. All the goddesses and their hosts, + wildcard Chihiro, + Haqua and Elsie, maybe Akari. 😉

If you were to go there and come back to me hurt, I will take your place.. and pull everything you hate.. into destruction...
I will erase anything that hurts you.. from the face of this world.