010. Years.
16. That number represented the number of years he'd been Shinichi Kudo.
2. That number represented the number of years he had been Conan Edogawa.
72. Based of the average lifespan of the Japanese male, that number represented the number of years he had left of being Conan Edogawa.
"I'm sorry, Kudo-kun," Conan's blood had run cold when she said his name for the third time attached to an apology. "There is no permanent cure, no scientific way to get your original body back except to just grow up again. The temporary antidotes are the best I can do, and even if you took them continually to stay as your teenage self, your body would build up immunity to them within one to two weeks. I'm sorry, there's nothing else I can do for you."
She had looked away from him after that, like she was afraid to see what expression or emotion she would see on his face other than shock. Conan was not sure what Ai had been expecting, but at that moment, he was unable to feel anything other than shock and disbelief.
He had always been absolutely certain that he would one day return to his life as Shinichi Kudo, renowned high school detective. Conan had always had faith in his own detective skills to bring the organization to its knees and Ai's knowledge of science to produce a cure. He had never prepared himself for the possibility of failure, and now, it was smacking him in the face.
In that moment, Conan wanted nothing more than to shout at Haibara and blame her for everything that was happening. But he couldn't do that to her. Maybe she had created the poison, but it wasn't her fault that he'd been caught unaware and drugged by Gin. Plus, she had done her best to find a permanent cure. It wasn't her fault that APTX4869 was one of the thousands of poisons on that planet that had no existing cure. So, he forced himself to remain silent as that first wave of anger washed through him.
When he was calm enough, he thanked her for the news in a hollow-sounding voice as he walked out the door. He had to get home before Ran noticed that Conan was gone. It wouldn't due to cause her any more heartache than he already had. After all, who knew how many years he would be living with here now?
In the days that followed, Conan quickly fell into a sort of apathetic haze. At first, Ran had thought he was just tired from all the excitement of the press and increase in cases at the agency. But those slowed down eventually and Conan's mood remained the same. Then, she'd been worried that he was suffering some form of childhood depression and took him to see a therapist. Of course, that hadn't worked, especially when the bespectacled boy refused to even talk to said therapist. Besides, he problem wasn't depression. He wasn't feeling sad; then again, he wasn't feeling anything at all.
Soon, everyone who knew Conan was extremely worried about the boy's welfare. The Shounen Tanteidan had gone above and beyond in their efforts to cheer him up. Agasa-hakase had made several new inventions for him. Kobayashi-sensei had called Ran several times to ask if anything had happened at home. Hattori and Kazuha made frequent trips from Osaka, and he had received numerous in-home visits from police offices like Satou and Takagi. Even Sonoko had expressed her concern, but none of it made any difference. Conan just didn't care anymore, and if they all didn't like it, well, they had years to get used to it.