The Pages '09 v4.3 Share > Send via Mail feature is no longer operational in Yosemite 10.10.3. You will need to export in the file format that you want to attach to your email, and then drag/drop that exported document into Apple Mail. Additionally, the installation of Photos in 10.10.3 now disables any access to pictures from the Media tool, so images will need to be drag/dropped, or inserted in Pages '09 v4.3.
Despite the above, Pages '09 v4.3 still has over 100+ features/functionality than Pages v5.5.3 on Yosemite. That means that if you open a Pages '09 document in Pages v5, what is not supported will either be mangled, or removed from the original document. And, the Pages v5 documents are not directly backwards compatible to Pages '09.
Not much of a bargain updating to Pages v5, which is not even based on Pages '09 v4.3.