Yukihiro is seventeen when his dream is crushed for good.
It suffers its first blow at twelve, when he's held back a year at the Academy; then its second and third when twice in a row, his team is rejected by their Jounin-sensei. The experience terrifies him, until he realizes that they're not expected to beat the Jounin, just to prove that they're not going to be a complete waste of time. The third time, he has the good luck of being teamed up with a Clan member who actually listens to other opinions instead of being persuaded that being bornmeans he'sinherently above commoners, and who agrees that tricks and traps might just be better than brute force when fighting a higher-level ninja is concerned.
Yukihiro is fifteen when he's made Genin. Their sensei is slow and easygoing; and he tells them that he chose them because their training will go the same way; slow and easy. Neither of them has the spark needed to go up fast and far. The best they can expect is Chuunin. Chuunin is good; it's a rank where you can be useful, without ever feeling the crushing responsibility of holding in your hands the lives of the whole village. Also, they will have a much better chance of living to raise a family. Yukihiro is starting to notice girls, so hey, it's disappointing but he'll probably live through it.
Yukihiro is sixteen when his teammates both pass the Chuunin test, and seventeen when, with another team that he doesn't know as well but goes along reasonably well with, he finally reaches the final stage. Then he is faced with true genius. Yukihiro is good with traps and his aim is reasonably accurate, but faced with a ten year old he can't even see move, he doesn't last long. He tries not to lose his head to pride; he could lift the child with one hand -- and then the child would kick his head clean off. As a result, he holds on a whole minute and a half instead of fifteen seconds. The child thanks him for giving it his best, and Yukihiro can't even hate him for it. Maybe next time, he tells himself, and almost believes it.
Yukihiro is still seventeen when the war takes a turn for the worse and they start using Genins in the field. Yukihiro is better at being sneaky than at confrontations. He's made a messenger. He tries his best but his traps are just blasted through and his scrolls taken. He's found hours later and summarily patched up and sent back to Konoha; a month later he will know that the information he guarded so fiercely was deliberately faked; the false information cost the enemy five Chuunins. They tell him he'll never run again.
He never does.
He was never a good ninja; a little cleverer than most, accurate aim, some skill with traps, and that's it. Basic taijutsu and low-level genjutsu were the best he could ever manage. But he already knew he would never amount to much, and girls like young, tragic war-veterans anyway.
He pities himself for a few months, fulfills the requirements of his doctors to the letter, doesn't tire himself out trying harder; his nerves are dead, he can't fight with half his leg numb and his kneecap smashed into nonexistence.
He lets girls pity him and care for him, and it's nice, except when it isn't. He can't drag himself out of his funk when everyone reminds him how deep he is.
Hana cares for him when he hurts and snorts at him when he just doesn't want to try. Hana is appreciative of his ninja abilities when they're useful for a civilian, and politely uninterested when they aren't. Hana coolly refuses the bouquet of roses he gives her when she comes for his daily therapy, and blushes when he hobbles all the way from the sanatorium to her village with a messy bunch of wildflowers under his arm. Hana likes his handsome face, and teases him for his white hair. Hers is cherry-red and about as natural-looking as his own.
Their daughter's hair is pink, and when she decides that she wants to be a ninja, Yukihiro lets her; she hasn't fallen for one of his traps in years.