Learn Turkish: Gençler teknolojik aletleri çabuk kavrıyor; yaşlılara gelince, onlar bocalıyor. - The youth grasp technological tools quickly; as for the elderly, they struggle.

The pattern [Noun or Pronoun] + [Dative ending -(y)a/-(y)e] + gelince literally means "when it comes to [Noun/Pronoun]". It is the standard way to shift topics in Turkish, equivalent to "as for..." or "when it comes to..." in English. Here, yaşlılar (the elderly) takes the dative suffix -a to become yaşlılara.

Since yaşlılara gelince already introduces the elderly, why is the pronoun onlar (they) used right after it?

The phrase yaşlılara gelince sets the new topic, but the following clause still needs a grammatical subject. While Turkish often drops subject pronouns, including onlar here strongly emphasizes the contrast between the youth (gençler) and the elderly.

Why are the verbs spelled kavrıyor and bocalıyor instead of "kavrayor" and "bocalayor"?

This is a great reminder of vowel narrowing. The dictionary forms of these verbs are kavramak (to grasp) and bocalamak (to struggle). When the present continuous suffix -yor is added to a verb root ending in a or e, that final vowel narrows to ı, i, u, or ü. Therefore, kavra-yor becomes kavrıyor and bocala-yor becomes bocalıyor.

Can the verb kavramak be used for both physically grabbing something and mentally understanding it?