I'm crazy? I do not think no ... XD
Masaki must have 16-17 years, while Ginjo (I too liked to draw him in the young version <3 <3 <3) ... 14! <3
Why you ask?
Well, in my numerous reflection I came to the following conclusion.
But first: remember that Ginjo said to "know the secrets of the Kurosaki family"?
And the dialogue between Urahara and Isshin in chapter BeLIEve (477 if I remember correctly).
I know ...
1) Ginjo and Masaki were best friends.
2) Ginjo, succeeds thanks to the vicinity of her, can to see the souls and the Hollows.
3) After he met Masaki and Isshin.
Isshin explains the existence of the SS (and etc.) and the particularity of Ginjo: is a Fullbring but not only ... in him lies a latent power, but does not yet know about it.
4) After a series of events, Ginjo (16-17) receives Shinigami powers from Isshin, Isshin pretends to be dead (for x things) and start the relationship with Masaki. Ginjo comes into contact with the SS and became Substitute, Urahara teaches him Shinkai.
5) At birth, Ichigo, Isshin and Masaki ask Ginjo to get away for the consequences that the discovery of marriage Shinigami-Quincy might entail.
6) Ginjo (24) met a Shukuro.
7) Isshin asks him to go to find Kukkaku and Ganju. At least they have to know that he is alive.
8) Masaki dies.
9) After this event, Ginjo begins to doubt the SS and even spend two years before he finds out the truth (the functions of the badge and ... (Ukitake's true plan ???) 10) During the escape, the Shinigami try to kill him, Kukkaku saves him but lost her right arm.
11) Given the impossibility of removing the powers, Ginjo asks Urahara to seal them.
Apart from my long explanation ... I hope you like my art XD <3