He really should have rejuvenated at least into his early 20s. 10 years is not a long time, he's going to have bone problems in a few years if he's already over 60.
I understand that the reason he did not rejuvenate back into his 20s is because there are a lot of manga and manhwa out there where a 30+ year old man gets reincarnated into a much younger age, so this manga preserves some originality by keeping the geriatric reincarnator's age nearly the same.
It still is an unwise choice, he himself said that he didn't have bone problems until he was 70. Now there are countless places to explore and people to meet, but he's going to get older again very soon. His only hope is that magic fixes his osteoporosis, which he is going to develop again soon.