There is no way this old man will give him something for free. Peter knows this clearly. And, this skill is something priceless. Putting the impersonating part aside, just copying others' power is already good enough to be placed as a Legendary Skill.
Peter doesn't believe such skill will come at free.
Hearing his question, the old man suddenly made dark eyes and spoke "I am just an old man who can't accompany his granddaughter on her quest to reach the peak. Well, you are a very shameless person but your shamelessness is different than others."
"You care about your people and that's all I need. Giving up on this skill, I am taking a huge risk. But, I believe you are not the type of person who often breaks his promise. So, take my granddaughter with you whenever you raid the dungeon."
"You don't need to take care of her anywhere else. And, if she ever thinks she can do it without you, then it's okay to leave her alone."