Southern people screw up my methods because their typing tends to model their speech no matter what age range they are in. So, perhaps this function should have a domain of only members north of the Mason-Dixie line.As an overall trend, I find that people that use shortened versions of everyday vocabulary (not phrases) tend to be in their mid to late 30's. Millennials, as a group, show the most incidences of deleted or incomplete punctuation. Not using capitals is also common. The very youngest group, under 18, has a tendency to overuse punctuation, particularly exclamation marks, and leave off capitals.
All of the above is highly subjective and can't be applied to any one individual post. It's more of a quantification of someone's overall style. Other factors include what method they use to denote amusement, smiley placement and frequency, sentence modifier choices, and vocabulary used.