Enlarging I see 18 (heavy 1) but with a very faint outline of what could look like a 4, could just be the photo - the FindAGrave profile maker and photo taker for William are the same person she would have seen the stone in person.
I have some people in my tree from this general area but none with this surname. Article refers to him as a student about 2 years before death so if it is the same person would infer a younger person. Probate does refer to those named minors, no widow, appoints surrogate - no one shows at later probate date. Might be younger siblings/family members that he was responsible for.