Not really sure. He was known as Satao, and have tried to do a search using his name and find a few things more but they only say he was the worlds biggest elephant, without saying how big he actually was. Closest thing to measurements is saying the following on his tusks:
http://www.outsideonline.com/news-from-the-field/Worlds-Largest-Elephant-Poached-in-Kenya.html
Kenya has deployed significant personnel and resources to protect what are known as the last "great tuskers," large bull elephants carrying genes that make their ivory outgrowths reach weights of more than 100 pounds per side.
Then the following page (which shows a photo of him with his face and tusks removed) says he was at least 45 years old.
https://www.facebook.com/photo.php?....268100646626483.41921.260365420733339&type=1
Satao would have been at least 45 years old. During his lifetime he would have weathered many droughts and seen many other poached elephants, and he would have sired offspring that, given a safe environment to grow up in, may become tomorrows generation of great Tsavo tuskers.
Reading further into his story it seems like quite a sad one. As he seem to be aware that his tusks which should otherwise naturally help him, put him at a greater risk than others::
http://markdeeble.wordpress.com/2014/03/23/last-of-the-great-tuskers/
Other elephants stood sleeping, clustered in the shade of acacias, apparently unaware of the bulls approach. He didnt walk straight to water. It took him almost an hour to cover the final kilometer as he slowly zig-zagged from one bush to another. The glint Id seen, came whenever he turned his head and appeared to bury it in a bush. Each time he did, hed wait a few minutes, partially hidden, then continue zig-zagging upwind, scenting the air, to check there wasnt a poacher hidden at the waterhole.
I was mystified at the bulls poor attempt to hide until it dawned on me that he wasnt trying to hide his body, he was hiding his tusks. At once, I was incredibly impressed, and incredibly sad impressed that he should have the understanding that his tusks could put him in danger, but so sad at what that meant.