There seems to be an age break between making a smiley emoticon look like this 🙂 and like this (-: and I think it’s about age 20.

For me, the former is proper, the latter looks confusing and wrong.

Allow me to establish that my over-20 way, the :-), is most correct. Why? Because we are English speakers, descendants of Greek and Latin. We write and read from Left to Right, Top to Bottom. Therefore, starting on the left would be the best way of seeing something from the top.

For the latter (-:, it looks like it is starting with a frown, quite the opposite of its intended meaning. It requires a double-take and some backtracking to decipher.

Besides, if you go down the dark path, then your big happy grins :-D, turn into some kind of unibrow demon from the pits of Hades.