I notice the version in MacPorts is much older than the current stable kde version. Is this lag intentional or can I somehow install the latest version on OS X?

This will be because Kdenlive developers don't actually support the macports version. A macports enthusiast will be doing that. In this case it is someone with the user name mk !
It looks like the project is still somewhat active because last time I checked the macports version was still 0.9.8. Now at least it is 0.9.10. And it was updated only 4 months ago. https://trac.macports.org/browser/trunk ... e/Portfile

But going to the next version on macports will no doubt be a big job because it moves to a new version of the kde frameworks upon which kdenlive is built - the kf5 version of kde frameworks.
I do see that there is a macport for kf5 http://www.macports.org/ports.php?by=ca ... substr=kf5

0.9.10 is a very good version. So you can either be patient, try and bribe mk (if you can figure out who she is) or have a go at porting the current version yourself.