Are you talking about the 10 year time skip in the beginning of the manga? Or all the flash-backs? Neither take place in parallel universe, and the flash-backs are just flash-backs.

For the ten year time skip, Oz (the protagonist) barely spends any time in the Abyss, yet in the real world 10 years had passed. So when Oz leaves the Abyss everyone has aged 10 years except for him.

Does that answer your question?

so we never see Oz older?i think i understand what u said.