Learn English – term for not identifying with your current age

I believe the linguistic term the OP is looking for is asymmetries

(with minor corrections)

Language and Sex Differences
^{Serap Yelkenaç}

... Moreover, another lexical fields that are taken into account as errors resulting in discrimination in language are marital status, asymmetries ( in other words, marked and unmarked forms), jobs and pejorative words about women. [...] For example; even though a governor is the one who governs a state, a governess means one who looks after children. In addition, a mistress is not a ‘female master’ nor a majorette a ‘female major’. For instance, while Mary is called ‘Tom's mistress’, Tom is not called ‘Mary's master’. You can say Mary is ‘Tom's widow’; whereas, you can not say Tom is ‘Mary's widower’.

The same term is used in An Introduction to Sociolinguistics
^{By Ronald Wardhaugh, Janet M. Fuller}

We can see this in some asymmetries of pairs of words. While actor and actress or waiter and waitress have few, if any, differences in connotation aside from sex, pairs of terms such as master—mistress, governor—governess, and bachelor—spinster are different in more ways than simply indicating male and female. While a master is the man in charge, the word mistress is commonly used to refer to the female lover of a married man. [...] While bachelor has connotations of fun and independence (as in the term bachelor pad) spinster is an undeniably negative term, calling up the image of an elderly woman living alone with lots of cats.) The interesting thing thing to note about these asymmetries, however, is that probably most readers of this text do not use words mistress, governess, or spinster at all. If they knew these words, they may not be familiar with the connotations cited here, as societal changes have made these terms less prominent and relevant, especially for young people today.

Further examples taken from a paper entitled
Language and Gender
^{By Suzanne Romaine}

2.1. Asymmetries

... Sir is still used as a title and a form of respect, while a madam is one who runs a brothel [...] In italian the related word maestro can mean a ‘schoolmaster’ as well as a ‘great teacher’, whereas the feminine form maestra refers to a ‘schoolmistress’. There is considerable discrepancy between referring to someone as an old master as opposed to an old mistress.

cradle-snatcher
someone who has a romantic or sexual relationship with a much younger partner _{^{(thefreedictionary.com)}}

You could try forcing a "neologism" such as juvenophile, but any term with this general sense is likely to be derogatory and/or humorous.

Noting @James's simultaneous post with an unfamiliar (to me) alternative version, I should just add that both forms apparently coexist in AmE, but cradle-robber is virtually unknown in BrE.