Yes, it is. However, this meaning of the word is rare. It is somewhat formal and old-fashioned. You would not hear it often in conversational US English. Usually, "frequent" is an adjective meaning habitual, regular, or often: "Sunsets are frequent occurrences." However, "to frequent" can also be a transitive verb. "to frequent X" means to be a habitual or regular visitor to a place. You "frequent" something if you visit it frequently. In everyday speech, instead of saying "I used to frequent Paisan's restaurant," you would be more likely to say "I used to go to Paisan's all the time," or "I was a regular at Paisan's."

"There's a little shop on the corner, which I frequented when I was a kid. I used to buy candies there. " Is this bit of text grammatically correct? Yes. You can use "frequent" to mean "visit frequently" or "visit regularly". He frequented italki and several other websites.

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Looks good to me.👍🏻 Another example: “Do you still frequent that barber shop?” Although it is correct, using frequent as a verb feels a bit formal to me. Probably would hear, “do you still go to that barber shop?” much more often.

Yes