For Intotheknight
Gabriella Wilde
Age: 27 [sorry her age isn't as close as you wanted, but more options below will be younger :) ]
Gifs: quite a lot
Known for: She's an actress and she's been in Endless Love, Carrie, The Three Musketeers and Squatters.
Other options:
1. Nicola Peltz [already mentioned in this book, age: 21, actress]
2. Maika Monroe [age: 22, actress]
3. Abbey Lee Kershaw [age:28, model and actress]
4. Olivia Holt [age: 18, actress]
There is also AnnaSophia Robb who has been mentioned before :)
Hope this helped!