Or more likely the person didn't initially SAY they were underage, from my experience if someone goes into a sex channel and claims to be 15 they are a much older adult, and if they really are underage they lie and say they are older. I have spent a fair amount of time over the years in some *very* rough sex oriented channels that were strictly 18+.
Since these were small channels with regular visitors the odd underage individual ALWAYS stated they were adults, if they showed up and said they were 15 they would have been kicked out in a heartbeat. If it came out 2 years later that a well known regular was actually 16 then often nothing was done about it but it was kept quiet (unless they were young females messing around with much older men, that was sometimes seen as too risky). After a couple of years they were as corrupted as they were gonna get, and they had friends in the circle, and everyone knew they weren't LE.
I personally doubt if a real 16 year old girl would be sexting with JH for 2 years, most 16 year old girls would not have that much patience, they would get involved with someone new. Regardless even if the person was really a 40 year old truck driver if they SAID they were a 16 year old girl it would still be a crime for JH to sext them.