Actually, in WN his skill is explained a bit more detailed. Alongside what is written in manga:
1) There is also manacost along with usages per hour. One of the reason he does not make himself younger is that his manapool will be less = less restoration uses, even if he could potentially use it 10 times per hour because of his soul remains the same
2) He can't rewind anything that had not been in contact with monster. For example, beds ^_^ He can't even rewind himself to the past before he first encountered monster - 15 yo.
3) He can't rewind memories (maybe yet)
1) There is also manacost along with usages per hour. One of the reason he does not make himself younger is that his manapool will be less = less restoration uses, even if he could potentially use it 10 times per hour because of his soul remains the same
2) He can't rewind anything that had not been in contact with monster. For example, beds ^_^ He can't even rewind himself to the past before he first encountered monster - 15 yo.
3) He can't rewind memories (maybe yet)