Here are some actors under 25 with natural red hair, besides Rupert Grint:
Currently Active
* Sophie Turner (27): Best known for her role as Sansa Stark in "Game of Thrones."
* Isla Fisher (47): Although she's slightly older than 25, she's a well-known redhead and her career began when she was much younger.
* Ed Sheeran (32): While primarily a musician, he has also acted in a number of films and shows.
* Devon Sawa (44): He's also slightly older than 25 but has been acting since he was a teenager.
* Christian Serratos (32): Known for her role as Rosita Espinosa in "The Walking Dead."
* Karen Gillan (35): Another actress who started young and has a distinctive red hair color.
* Jack Dylan Grazer (20): Best known for his role in "IT."
Less Known But Up and Coming:
* Willow Shields (22): Known for her role as Primrose Everdeen in "The Hunger Games."
* Charlie Heaton (30): Known for his role as Jonathan Byers in "Stranger Things."
* Jacob Bertrand (26): Known for his role as Hawk in "Cobra Kai."
Important Note:
* While I have included actors who are slightly older than 25, I've tried to focus on those who began their careers at a young age or are currently considered up-and-coming.
This list is not exhaustive, but it gives you a good starting point for some talented young actors with natural red hair. Let me know if you'd like more suggestions or have specific criteria in mind.