Not really, if the body was made from scratch to look 17 that doesn't mean it actually is 17 the second it starts to exist. A better argument might've been adding on her age from the first life, which should have been in her 30s-50s I guess? Forget what it said or if it even did. But that seems up for debate too. A lot of how you think and feel will depend on your brain chemistry more than the actual amount of time your mind has been cognizant. Someone who isekais into a child's body should absolutely be affected by their child brain and not necessarily always act appropriate to their original age.
@ esp
Major plagues happen around every 100 century and smaller plagues around every 50 (not concrete, just a approximation) so around ~6 ish, I would guess.