Some people think regular chicken mating is brutal and mean, when it is actually natural. When either the male or female are young, it does not always go as it should. In a normal mating:
1. The rooster dances (drops his wind and sort of circles around a little) to signal his intentions.
2. The hen squats. This gets her on the ground where the rooster's weight is spread out. If she tries to stand up, the weight might be too much but if she squats, the weight is not all that much for her. Roosters of the same breed as the hen are almost always heavier than the hen. Their mating technique makes that no problem.
3. The rooster hops on and grabs her by the back of the neck. He is not holding on for balance. He is not trying to hurt her. Him grabbing the back of her neck is her signal to raise her tail out of the way. That is how she knows to get ready.
4. His vent very quickly touches hers.
5. He hops off. The hen stands, fluffs up. and shakes. This fluffy shake is not her telling him, "That ain't nothing, Big Boy". She is actualy positioning the sperm to where it needs to go in her internal egg laying system.
Sometimes, when the rooster dances, the hen tries to run away. The rooster may ignore her. This happens a lot with my flock.
Sometimes, when the rooster dancers, the hen runs away. The rooster chases her. The hen quickly squats. She was just teasing him to see if he was serious.
Sometimes, when the rooster dances, the hen runs away. The rooster gives serious chase and eventually catches her. She squats.
In all of the above, no harm is done to the hen.
Sometimes, though, the hen never cooperates. The rooster, being bigger, can force her. Sometimes hens just refuse to accept any rooster's advances. These do not make my permanent laying/breeding flock. Sometimes, the rooster is not mature enough or dominant enough for the hen to accept him. Sometimes the pullet may be immature and not ready for any rooster. Sometimes the rooster is a brute and does not deserve to be round any hens.
Often, when I have one or two hens that are having problems with a rooster, I eliminate the problem hen. The other hens do not have any problem with that rooster. Peace and tranquility is restored to my flock. In these circumstances, I do not blame the rooster.
Most of the time, the problems are greatly magnified when they are young. The young immature rooster has his hormones driving him crazy. Mature hens expect a rooster to behave in an acceptable way and have no respect for the young upstart. Immature pullets mya just not be ready for him, yet his hormones are really controlling his actions. A lot of the time, the rooster or pullet will outgrow adolescence and act like mature adults. But some roosters remain brutes and need to be disposed of.
From the ages you mentioned, I think the biggest problem is that your pullet is just not quite ready, but is getting fairly close. At least close enough that the rooster can tell she is a female, not just a chick. And his hormones are hitting him hard. As long as there is no blood or wounds from spurs or claws, no real harm is being done. She will probably be laying in two or three weeks and may begin accepting his advances. Your best course of action is probably to watch for any injury but just to let them be and let them work it out. Chickens have been growing up for thousands of years. This type of thing is pretty normal.