" . . . and in this particular case it seems unlikely to me that it was a teenage male. . . . "

Teen age male or male in early twenties is statistically favored for sex crimes and perhaps for murder, though not necessarily murder of young children.

I however think the note writer is older, more-experienced.

I also think that anyone who would have any sort of grudge against the Ramseys would tend to be older. Some panhandler perhaps? Recall that Gary Oliva was charged with 'aggressive panhandling'. Did he take offense to someone's reaction to his aggressive behavior. One mugger once said '' I shot him because he didn't give me my money fast enough'. My money! That would be the Demented Creep type. However, I think the Bright, Personable Chap is more likely to write that ransom note and have all these 'creative' posings and false indications.