Should I abandon an open math problem, if it hasn't been actively studied since the mid-1980s? There is an open math problem that I am interested in. There was a lot of progress in fully working out the problem in low-dimensions and progress towards sub-problems of the main question up until the 1980s, but it seems that the research activity has mostly stopped since then.  Newer papers just essentially reiterate previous results.

A pretty well-known professor in my department also published a few papers on this problem in the mid-80s, so I reached out to him and told him that my thesis adviser and I are currently studying this problem.  He confirms that his work on the problem is very old, so I'm guessing he hasn't done anything newer with the problem since his last papers.

The problem itself is known to be quickly intractable for higher dimensions, say, for n>5.

I'm taking his words as an indication that there is not much interest in this problem, and that I should probably abandon it and find another problem to work on, for my master's thesis.

Am I making the correct interpretation of this professor's remark?

Should I still stick with the problem, even though it might be true that it is not currently being actively studied?
Based on your brief description, I'd say a more likely explanation for the lack of work on this problem is that people are stuck. Not that there's no interest in it.

Still, I wouldn't recommend this problem for a masters' thesis (or a PhD thesis). At least at the start, you should work on something manageable. If you hit a manageable problem or two out of the park, then you can start trying things professional researchers have attempted and failed.