If you watch closely the last panel, that one where they’re both hugging you’ll see the wrinkled arms and hands of her (the FL).
I think what happened was that when both saw each other they immediately saw themselves as their younger version as if the time had not passed. Then when the conversation is over and they hug they show us (the readers) the characters’s present selfs and we see they’re both old. Meaning that a lot of years passed and they’re reuniting just then and now

I am a bit confused with the ending, surely shinpei was alucinating?
She was young while he was old so she definitly died that day, and he was just imagining her right? Im left speechless, lend me your thoughts mangago folks ╥﹏╥