IMHO they are not easy to keep, judging from so many cases or people having problems with them sooner or later. I don't recall a single report here on MFK of someone keeping a gulper for 5-10 years at least, except maybe Koltsixx.
My trio is 3 years old --
https://www.monsterfishkeepers.com/forums/posts/7630190 -- and I am having an unknown problem with one of mine. It's stopped eating and wasting away, has problems swimming up right. Been like that for a month or two now. The other two have been fine. I don't know if the struggling one is the one that had eaten (and digested seemingly fine) an equally sized 4-line pim catfish of ~9". If it is that one, the spiny pim might have damaged its internal organ and this is the result.
Pretty much 90%+ of gulper threads end rather soon with keepers reporting their fish having skin problems or wasting away. Most of these issues appear to stem from their need for water on softer and more acidic side versus the opposite. Most people's water in the US is rather hard. Some issues appear to be caused by people giving them live fish to feed on, which, given their weakened immune system versus their wild kin, sooner or later leads to an illness.
In general, they are not said to be a beginner fish at all but a specialty fish.