I actually think that [name]Sage[/name] can still work for a boy! I know a little boy I believe about eight years old named [name]Sage[/name], and he rocks it. So, you might not want to check it off your list completely.
I would assume Osage was pronounced either oh-sayge or oh-sahge, but I did a tiny bit of research (aka googled it) and found that it is the name of a tribe pronounced Oh-sa-ga. Since you have no relations to this tribe, I think it might be a little insensitive to use it. However, the name [name]Dakota[/name] is very popular, and I believe that is also the name of a tribe. Ultimately, its your call, but I wouldn’t personally use it.
What is it about the name [name]Sage[/name] that you like? The fact that its a short ‘S’ name? Or the ‘age’/‘ay’ sound? Here are some ideas based off of those two “parts” of [name]Sage[/name] (please ignore them if you don’t want any suggestions):
[name]Shai[/name] (pn Shy)
[name]Gage[/name] (ooh, I think this is great. It has the simplicity and sound of [name]Sage[/name], but is clearly masculine)
[name]Hope[/name] this helps.