If the descentralization of social networks continue, we will have to prepare for the eventual rise of the instances wars, where people will start to fight about which instance is better and which one is weird to be in and so on, but that’s for the future of us all.
Yes, age alone shouldn’t lead to getting blacklisted. But if an instance is two days old, already 50+ accounts from there were banned on your instance for being bots and besides that there was no real contributions coming from that place, this might be a candidate for auto-blacklisting.