u/paulili

We know Emilia got her looks mostly from her father's side, who is assumed to be a full elf. She got her kind face from her mother, which is the only resemblance to her. Since her father is a full elf, he is technically immortal. Fortuna's age is also unknown, but she is probably the younger sister to her brother. Their parents are full elves, so they could have had both children at any point in time.

Satella and Emilia look very similar, but I think Satella doesn't have Emilia's kind face. This could mean they have the same father, but not the same mother. Since their mothers were both humans, they obviously would have died due to age or in an accident.

What's also interesting to me is the resemblance in some elves, who can inhabit souls and witch factors. Some prime examples are Fortuna (possibly Sirius), Satella (WoE) and Shion (Lilac).

EDIT: Some contradictions/additions:

Puck and Echidna seemed to know of Emilia 400 years ago. Puck was created and tasked by Echidna to protect Emilia.

Puck is probably Emilia's father turned spirit.

Emilia's parents could have died/disappeared in any point in time, hints going towards Pandora killing them.

Emilia's real age in unknown, except to Alec Hoshin and maybe Echidna.