No, you are not shallow for wanting to look nice IMO.
I was 12 in !963 and told that any girl could look well-groomed by making sure that she and her clothes were clean, nails filed, stocking seams straight etc.
Later I realised that the quality of the clothes has a lot to answer for too.
All my life, I have felt more confident if I felt I was looking, perhaps not my best, but as good as possible.
So find yourself that hairdresser and perhaps a beauty parlour as well.
Now is the time to go through your wardrobe too, and get rid of anything that makes you feel old, tired or dowdy!
Let's age with style - like the grandmother in Chocolat who wore red silk undies because she was always in mourning black as regards her outer layers of clothing.