Definitely!
We have no idea how long it takes the OP’s son to drive 5k miles. What if his driving patterns mean that he only drives 5k miles per year, with mostly short-trip local driving?
My suggestion is to do 2 or 3 oil changes at 1 month intervals, in the hope that this will help to rid the engine of the gunk that has accumulated over several years of “extended” oil changes. If the oil looks reasonably clean after 2 or 3 of those one month oil changes, then I think it would be safe to go to longer intervals.
However, we still don’t know whether the OP’s son drives 5k miles in one year, or in six months, or…? At the very least, he needs to change the synthetic oil at least once each year after those 1 month oil changes, but more often is certainly better. Personally, I won’t go more than 5-6 months between oil changes.