Judge your audience or group of people. If there are older women present you might very well confuse and or insult them by calling them 'guys'. Feminist young women are likely not to tune into what you have to say, having called them 'guys'.
You know what, if in doubt go back to greeting a group of people whose opinion you value by the old fashioned but all encompassing SAFE, "Good morning ladies and gentlemen." A big smile will soften the formality of your opening words.
As a retiree I'm amused to be called a "guy, a girl, lady! etc" I can't waste a single moment picking up offense. It is largely the manner in which any of these words are used that denotes respect or lack thereof.
I walk briskly away from anyone who lacks respect. Why would I want to interact with someone like that when the world is full of lovely people who want a good old fashioned chat.
Interesting topic.
As a retiree I'm