Well, It seems jinchuuriki get the same power as their bijuu(e.g gaara's sand from shukaku, roshi has son goku's lava style). since the sage was the Juubi's jin for the rest of his lifetime after he sealed it, he must've at least gain the ability to use mokuton. so its not a far fetched possibility...
No, it isn't. It is possible.
However, We dont know how long he was the jinchuriki for. For all we know, he spent a day as the jinchuriki before he got bored, split it into the bijuu and sealed the Mazo in the moon. All we know about that feat was that he did it on his death bed. Who says he wasn't dying of Bijuu Extraction? He could have sealed it, Immediately split it into the bijuu, Created the moon and Died.
Just because he appeared old doesn't mean he actually was. Tsunade looks much older than 50 when she is out of chakra. Nagato looked old when he was out of chakra. It could just mean he was out of chakra from all the Bijuu making and Moon sealing.
Anyway, Regardless of whether he has SM after becoming the Juubi Jinchuriki, he Definately didn't before, which is what we are talking about.