It's not that your getting old, It's because the brain sees what it expects to see. That's how I read it the first time I looked as well 
It may have been an E Mail I got but I remember seeing an article about this that contained a sample paragraph where the spelling was all messed up, but you could just read right along because your brain straightened it out. That's why hunters have to learn the difference between "looking" and "SEEING".
if yuo can raed tihs, you hvae a sgtrane mnid, too.
Can you raed tihs? Olny 55 plepoe out of 100 can.
i cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it dseno't mtaetr in waht oerdr the ltteres in a wrod are, the olny iproamtnt tihng is taht the frsit and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it whotuit a pboerlm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Azanmig huh? yaeh and I awlyas tghuhot slpeling was ipmorantt! if you can raed tihs forwrad it.
If you can read this, your brain is 50% faster than those who can't.
http://www.funny-potato.com/read-this.html