In chapter 88 she playfully tells Nasa that her body doesn't get sick or injured and seeing how in the first chapter after Tsukasa got hit by a truck, she's gone for a while and seen again in the next chapter with no injuries what so ever. it's implying what she has said seems to be true.
in chapter 92 there's a flashback where we see an injured little girl walking barefooted in a destroyed unknown city, most likely either Hiroshima or Nagasaki, there the little girl met an unknown woman that'll help her. then after the flashback ends, we got a paralleled image of Tokiko and the unknown woman. because I'm dumb, at first I thought the unknown woman is Tokiko which is impossible, considering the bombing of Hiroshima and Nagasaki is in the 45 and the setting of the story is in 2019 (there's an endgame movie reference and endgame released in 2019). I strongly believe that the unknown woman is actually Tsukasa-san, even though it's a baseless assumption. I do believe that Tsukasa is an immortal being and already existed for a long time ago. She said she's 16 but has difficulties in handling her smartphone (she's even forgetting her own phone password), but somehow she's very proficient in handling old game console. there's also how casual she is toward her should be grandmother, Tokiko-san, calling her by her given name not grandma or obaa-chan/san/sama. so it's either she has a very bad relationship toward her, or she's actually older than her.
in chapter 29 she can read what it seems to be an ancient Japanese letter, and she has the ability to wield a katana. remember she said she's 16 and how could a mare millennial do this?(yea it's a prejudice toward myself). so either she's educated in a super traditional way by her family or she got from her own experience (if she's an immortal that already existed form time unknown). considering how Tokiko herself could do programming in c, I don't think that the Tsukuyomi family would be educating their family member in a really strict traditional way.