Is it offensive to get ID'd at the cinema?

Okay so I'm 18 years old soon to be 19 and the other day I went to the cinema to see a 15R movie. My friend and I got stopped at the desk and asked for our ID, which I was shocked about because it's only a 15 and surely we look older than that... Does this mean we both look younger than 15 or do they ask pretty much everyone for their ID?
Is it offensive to get ID'd at the cinema?
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