Nice shirt! I see a collar button loop and what looks like vertical buttonholes, both suggestive of pre-1970s. The chest pocket is also cut so the print matches, which is generally a good sign. What are the inner seams like? Flat felled like blue jeans? Or serged? Earlier and/or better made shirt are usually flat felled or French seamed.
I did come across one Royal Surf women's shirt on Etsy with this tag - the seller dated it to the 1990s, but I'm not clear why.