Credit for chart I've modified: @arcange
I like to think of Steemians in terms of generations. I don't know if this is a useful way of thinking, it may or may not, but I'm going to present it anyway.
Steem has followed a pattern of waves and troughs. This pattern is present in the price and adoption of most cryptocurrencies, but with the social network aspect of Steem and greater actual usage, when individuals joined the network is both more visible and has a sense of importance on Steem. We see the same waves and troughs in every chart of activity on Steem, although to different degrees for different metrics. For example in the chart above, you can see that posts tend to decline in a trough much more than active user count (perhaps due to the impact of bots).
There have been 3 clear 'waves' in the history of Steem so far. They started in July 2016, May 2017 and December 2017 respectively. Each wave has lasted about 2 months, with a longer lasting 'trough' of declining activity that follows. This pattern is not the norm among successful social networks, but Steem being just as much a cryptocurrency as a social network, it can be expected that this is the pattern of growth, given the financial feedback loops inherent to cryptocurrency.
The waves result in 4 clear generations.
Generation 0 are the Steemians who were here before there was any major wave of users. They may have been following Steem from the launch thread on Bitcointalk, or got involved via trading or mining. Many of them predate even the social network site Steemit.com as users. The number in this generation however is tiny. The surge began a few days after the first payouts were made on July 4th, when there were about 14,000 accounts, most of which were likely duplicates owned by a much smaller number of people.
Generation 1 are the Steemians which arrived amongst that first wave of users. Most were likely already in the crypto space, and can now be considered crypto veterans. At the time they were just people excited by the idea of a decentralized social network, one which pays users and actually works. Almost no cryptos outside of Bitcoin had any 'working product' at the time. In fact most of the cryptocurrencies at the top today did not exist at this time, it was still the time when 'altcoin' meant a direct fork of the Bitcoin software with superficial changes if any. It was also during a crypto bear market, following the collapse of the DAO of Ethereum. The wave was extended by the arrival of @dollarvigilante in August, who brought along a large following of anarcho-capitalists.
Generation 2 arrived (you guessed it) with wave 2. At this point Steem had already had most of the largest changes that have happened to the protocol. For example, the supply curve of Steem had been changed from hyperinflationary liquid Steem to a disinflationary curve. To this day many people believe Steem is hyperinflationary, despite the vast majority of users only having experienced the newer curve.This generation also came after @dantheman had left Steemit a few months before, so for most users @ned has always represented the 'leadership' of Steem via Steemit Inc. Importantly, this wave occurred following the 'whale vote experiment', where @abit and @smooth enforced an effective rulechange for the issuance of Steem via the reward pool. By countering the votes of large whales, they linearized rewards, allowing ordinary users with small stakes to have non-trivial voting power, outside of voting for posts that were already popular. At this time the crypto bull market was in full swing, although it was a few months still before it peaked.
Generation 3 began to arrive around the peak of the crypto bull market. The actual peak of Steem followed 1 month after the peak of Bitcoin, but new crypto enthusiasts were discovering Steem at this point. It also represents a large influx of users from Korea, where Steemit.com was within the top 200 websites nationally for a time. Problems which had slowly arisen since the linearization of the reward pool were already clear for Steem at this time, with self voting and bid bots very controversial issues. Despite these issues, this was the largest wave of users so far, and brought Steem to the ATH that we've declined from ever since. Several Youtubers of much higher fame than prior waves joined at this time, and it was also a time of flourishing for dapps beyond Steemit.com.
Wave vs. Trough generations
Generations 1 through 3 can also be divided into wave and trough generations. For example Gen 1-Wave and Gen 1-Trough. 1-Wave would mean this person came in during the large wave of users at wave 1. Most users probably joined during these times of excitement in Steem. Gen 1-Trough would have come in the time following the wave, when Steem was already in decline. The trough periods last much longer than the waves, but likely represent fewer users. The sentiment at the time of joining was very different for wave vs trough, and that's why I would consider separating the generations further.
Thanks for reading, I hope this post was interesting and valuable to you. Here's hoping that wave 3 won't represent the final large 'generation' of Steem users, and generation 4 is just around the corner...