I'll even give you a linear comparison of the cast's ages.
Tian>>>>>>>>>>Oleander>>>Velvet/Paprika>>Pom>Ari
Their expected lifespans and maturity rates, however, differ according to species. A "wise elder" for the Cattle or Sheeple would in linear years be a youngling to the Longma, but already have kids and grandkids by the time a longma would end early childhood. If you were to order them by the "maturity" stage in their species lifespans, you'd get
Tian>>Velvet/Paprika>Oleander>Pom>Ari.
Although Oleander is technically "older" than Velvet and Paprika, she's just out/in the tail end of unicorn puberty*, while both Reindeer and Alpaca are considered "young" adults in their individual communities and species.
*She was 13 when she married pact'd with Fred, and 26/27 by the time of the game's plot.