I post mostly at night or in the morning, tiredness accounts for a good portion of my mistakes. Posting in a rush gives rise too many typo's as well, apart from that and comedic effect, you can argue the point that most browsers now have spell check, and Google has one built in. You're right on the point that with age comes better spelling and grammar. My old posts make me seem even more retarded and I'm guessing that if you spend most of the time you're writing in a formal classroom setting, then you'd be more likely to check as you go, while when on the internet things seem less formal, at first and you'd expect less people to care, until you realize that the only thing people have too judge you is what and how you write. final point I'd have to make is that syntax can be a pain in the ass for those who don't write often, or do so in sporadic notes, so many little rules and ways of getting an idea cross, the difference between 'too' and 'to', even when writing this I've had too make many little changes, re-order words and fix things that would only be noticed if everything was re-read, and chances are something will still not make crystal clear sense to those reading due to a misplaced comma or my ability to write paragraph sized sentences. that or a sizable portion of internet dwellers are retarded, possibly both.
"Time takes a cigarette, puts it in your mouth
You pull on your finger, then another finger, then your cigarette
The wall-to-wall is calling, it lingers, then you forget
Ohhh how how how, you're a rock n roll suicide"