Of course creating these life-like characters almost always involve drawing on the characteristics of real people. Clearly you can't create a character that's an exact copy of someone you know. (Unless you're writing their biography.)
I recently found myself in the (un)fortunate position of arriving at the airport to discover my flight had been delayed. Most people would get all in a huff about it. As a writer, it's the perfect opportunity for me to observe people's behaviour and study their mannerisms without influence. Being stuck at an airport for two hours is a great way to practice character development and building back story.
Is any of that true? Hardly. He's most likely a businessman going home after a long day and simply called his wife to let her know his flight had been delayed. So where did I get all of that back story from? As a writer, I made some simple observations:
1. He was dressed in a business suit,
2. had his laptop open on his lap,
3. was talking on his mobile phone in hushed tones,
4. and constantly checked the time on his wristwatch.
As for the rest - that's the back story I created for him in my mind.
Then there's the young woman with a toddler and a baby. She has her hands full with the toddler, trying to get him to sit still instead of running up and down between the seats. At the same time she's trying to appease her crying baby with a bottle. What back story can you create for her?
With people around us all day, there is ample opportunity to observe people's behaviour and mannerisms. You may even want to keep a little notepad and pen with you to make notes of things you observe people do. Just like the example of the businessman, only a few observations can help you create a well-developed character for your next story.