How can one get rid of a marriage that the questioner believes to be unlawful due to an age gap, and should the wife be confronted or abandoned?

If the marriage was without the guardian's knowledge and the contract was directly performed by a شيخ (sheikh) with witnesses and a formula ( صيغة), then it is a marriage where the guardian was absent. This is invalid according to the majority of scholars, but it can be validated by a judge's ruling or by following the Hanafi school of thought.

As for a true secret marriage (نكاح السر), it is invalid and must be annulled. According to the majority of scholars, this refers to a marriage without witnesses. According to the Malikis, it means a marriage where the witnesses are instructed to keep it a secret. The preponderant opinion is that of the majority of scholars.

If the marriage is invalid, one must distance oneself from the woman and inform her of the marriage's invalidity. The contract can be renewed with its pillars: a guardian, two just witnesses, a dowry, and a formula. There is no harm in her being older in age.