Maybe a longer life span for the nichelings?
like 1-100 days for baby & child, 1-125 days(maybe 150 max) for teen, 1-275 for adults and 35-450 for elders and maybe more?
Because not only you can have your little critters live longer but you can also have them be a baby longer (who wants to have a baby nicheling for 4x longer than adulthood? lol) and another age level, Elder; this can be used for like an extension to your nichelings otherwise "Normal lifespan", as long the nicheling doesn't have too much damage where that level is removed basically it could for like an extra 35 days to an already 200 day-old nicheling, there could be an option where either can be a breed-able age level (cats) or not (like humans for an example), sorry if this sounds confusing.
(another question, i wonder how you program age in niche btw, is it easy? hard? also i know this is just an idea but just something i wanted to suggest to the sequel.👍)
Edit: Elders should be at least a bit weaker than adults and teens.
Another Edit: I Think the modding thing's cool too!