The first sign that you are emotionally mature: you acknowledge that no one ever truly is.
The generative discontinuity of insecurity is very much the mischievous absence around which we build our subjective selves and each iteration of developmental sedimentation into (and as) memory, experience and learning only ever really amplifies this uncertainty in useful ways. From logic to language and from experience to self-determination, it is precisely the absence of developmental closure that provides us the ability to grow and adapt.
Maturity is perhaps a matter of patience and acceptance that dissipative disorder and disappointment are irreducible components of experience and identity. Without accepting that even maturity as a concept or aspirational emotional and psychological state of constructive engagement with a thoroughly stochastic world is subject to the entropy endemic to this Universe and all embodied existence within it, we will become much likely to encounter the snakes rather than the ladders of positive personal, interpersonal and planetary civilisation growth.