Yep! But what I meant is not when Haibara turned back into Shiho. She will relive her life again as an 18 year old again and mitsu-chan will be 18 year old as well.
And there is no problem with an age gap like that. In Japan, it is way too common for a guy to marry a girl way older than them. Anyways, girls in Japan tend to look younger than their age. Whats so "uncute" about that?
What I meant by cute is their characteristics. They will be a little bit like Sato and Takagi Except Shiho-chan would be a "quieter" version XD. Mitsu-chan will grow up to be a very mature boy even at 18 and prob become a detective as well XD