Red Riding Hood’s age is never given, yet we know she is old enough that her mother felt confident in allowing her to trudge through the woods alone to her grandmother’s house. An estimate of 10-12 years old would not be outrageous. Certainly, she would be able to know how to get to Grandmother’s house without getting lost along the way.
This is only an estimate, but fits with the circumstances, though the age could be up or down by a year or two. This age in the story is not the same age as we would treat it, today. Though Perrault and the brothers Grimm published the story well past the Middle Ages, the story was known well before then. Enough variations of this story exist from Germany, France, and Italy to reliably state that this was a tale known throughout all of Europe, likely for hundreds of years. This would place the story well before the Italian Renaissance, firmly in the Middle Ages.
Not only is this world full of natural dangers from untamed forests and wildernesses, it is rife with outlaws and bandits who prey on travelers. Furthermore, there is the threat of the plague. The black death ravaged Europe several times through the centuries, driving down life expectancies. The age of what was considered marriageable—an adult—was quite young.
For girls, especially, this was an age where they first experienced tangible proof of their adulthood: menstruation. After their first bleeding, they are a woman and fit to be married as they can now bear children. This can range from as early as age 8 to 15. This would put Red within the range of being marriageable. The story is full of imagery focusing on the color red—symbolic of blood and passion—and picking flowers. Together, these are a subtle clue to the deflowering of a virgin.