we know Tsunade is in her 50s and she remains youthful with her seal on her fourhead but it is my opinion that she should actually not look so haggish for a couple of reasons
1. she is in her 50s not her 90s her appearance when weak is that of a frail old lady and i mean old old lady, look at orochimaru and Jiraiya both look at most 50 but neither of them are as old looking as her when weak. 2. she is an uzumaki and as such has the strong life sustaining chakra and life force. she should naturally age slower than others. as such shouldn't she naturally look as young as she does.