Realisation that one is trans can take anywhere from a few moments to several decades. Sometimes trans people have an inkling early on in their lives that their assigned gender feels out of sync with their bodies sometimes this doesn’t come to light until much later in life. The self-realisation process can be extremely complicated and scary.
The human mind does its best to help us survive, which can translate into triggering intense denial. Due to the gender binary and fear of being ‘abnormal’, it is common for a person to try to ignore signs pointing towards gender variance, whether consciously or unconsciously. Coming out is an incredibly personal thing, if someone comes out to you, make sure you offer them confidentially, support and reassurance.