Let's say we run into some other species will they accept a 95% premined supply?Yes bitcoin is 95% premine to anyone coming into contact with it for the first time today.
Obviously other species will accept BTC, BTC is boundless anyway, Alien will take advantage of this feature to establish a form of trade to human kind.

. About being premined, why not, many investors had been accepting 100% premined coins and tokens, and I think this alien won't mind.
Chances are they are more advanced than us let's say
Do you think the aliens will accept bitcoin
In order to establish trade the one with more advance way of thinking will step down to the level of knowledge of their counterpart before introducing their advance means of finance system.
What about newborns?
This answer suits the question

Maybe if newborns have the capability of understanding money (or handling a smartphone) in the first place.