Clearly human infants imitate the behavior they see in the environment as a means of learning as doing so increases fitness. The idea that there would be a tendency for absorbing certain behaviors more from those with similar sex traits than those with different because it increases and decreases is not so strange.

Golly, you've clearly not spent much - oops, I mean any - time tending to human infants, have you? Infant humans imitate the behaviors of others they see and who interact with them, and especially those who lovingly care for them, coo at them, smile at them, talk and sing to them, play with them, etc - it's called "mirroring." But human infants do this regardless of the sex, age, race, ethnicity, hair color etc of the people who interact with and care for infants.

Human infants do not choose to model their behaviors only on those with "similar sex traits" to their own coz infants are unaware of their own sex and sex traits. Human infants can discern the differences between male and female voices, and other differences between mom and dad, men and women, that adults and older kids know to be linked to sex. For example, an infant who is exclusively breastfed quickly learns that when they are hungry, it's their female parent they need. But infants don't know that sex-linked traits are indicative of sex coz they don't have the intellectual or language capacity for such complex kinds of thoughts yet. Coz they're babies.

Sex is based on anatomy not gametes or else people without gametes are sexless, and the anatomy that constitutes sex occurs in a variety of intermediary forms and combinations making sex a spectrum

Sex anatomy is determined by which of two distinct, typical pathways each human has developed along. Except in very rare cases, males will have the potential capacity to make male gametes, sperm, at some point in their lives. Except in very rare cases, females are born with all their female gametes, ova, already formed, and once they reach menarche, females will have the capacity to mature and release female gametes on a cyclical basis, usually once a month, over a span of time usually lasting 40 or so years (commonly from circa age 11 to 51).

Gametes are made by male and female gonads, which are the testes and ovaries respectively. Testes and ovaries are entirely different. Except in cases of ovotesticular disorder - which is extremely rare, and which does not result in the production of viable gametes of either kind - males and female gonads do not exist on a spectrum, no there is no overlap between them. Similarly, the gametes produced by male and female gonads are also entirely distinct and different: sperm and egg. Those two are the only kinds of gametes that there are; there is no spectrum of gametes.