How 30-50 year old Japanese male would say hello to another male colleague in same age in same organisational level in IT company? I'm looking for everyday based not formal way to communicate.
my colleagues always say おっす to me
おはようございます and お疲れ様です are still the most common choices. But the actual pronunciation can be heavily slurred depending on the politeness level, and it may sound to you almost like "おやざーっす", "おつかさーっす" or even "おわーっす". After all, you say it every day, and everyone can understand what has been said.
おっす is usually used between close friends outside the office. It may be acceptable depending on the atmosphere of your office, but you should not be the first to start using this.