What you list are common characteristics encountered in legacy systems, but what makes it legacy is a business decision of declaring it obsolete and in maintenance mode, and so that no money or time to be invested in it. Old systems that continues to evolve are not legacy, like say Linux, and yes like you say a project that is only one year old can be declared legacy. Resistance to change is only an economic variable that drives the decision. Vibecoded apps fits the definition because the developer is unlikely to want to invest more time in them for different reasons.