Can't really comment as daughter first encountered tights aged 6, but,I've seen girls of 5 manage without help. Practice is possibly the key, or, familiarity. Here in Switzerland tights are essential in winter.
She is just going into the third year of maternelle and will get into big trouble at school if she has to ask for help in dressing. I have only bought clothes I am 100% she can manage with ease (long sleeved t-shirts, elastic waisted skirts, velcro-fastening shoes, buttoned coat...) - it's just the bleeding tights she can't get her toes into on her own!
DD wore tights to school from reception onwards, I know that the assistants never helped them get changed after PE etc. So she has managed tights from when she was just coming up to 5. She did come home with them on inside out many times.
FWIW I found that thick ribbed tights were a lot easier for her to put on than the smoother tights, they seemed less, um, tight.
Buy them a bit big and teach her to stretch them out well. They're much easier to deal with when they're a bit loose, plus they will go up all the way. Thicker tights do work better, even though they are bulkier for little hands to handle. And they are much warmer, and usually made of cotton or cotton blend.
I found some tights were looser and easier to pull on. Once my DD figured out that once she had got her toes in, she had to pull everything up from her ankles, then from above her knees and then the waist, she was fine.
For awhile she was sporting the attractive gusset just above knees look as she was only remembering to pull them up from the waist.