young girl (of 14, 15 years old)

not ... at all

even if ...,...cannot

to mature / to ripen

maturity / ripeness

very, exceedingly, awfully / (before a negative form) not at all, at all, by no means

negative continuative form of かかわる

although

Alternative form of 関わり

to be in relation to, to be relevant to, to be involved in / to be involved in a negative way: to meddle, to interfere / to have a substantial effect on something, to endanger something