Jamie Martin, Assistive Technology Consultant for Students and Adults with Dyslexia
As Lisa Friedman mentioned, dyslexia can certainly be identified at any age. Just ask Steven Spielberg, who lived 60 years of his life before being formally identified!
Because every person with dyslexia is different and has varying degrees of language difficulties, some people can make it through school without it being detected. That's because some dyslexics can use strong higher-order language skills to compensate for low-level deficits in reading and writing. Brock and Fernette Eide call this "stealth dyslexia." You can check out a complete explanation here.
The good news is that it's never too late to do something about it! Teenagers and adults can receive language remediation and start using assistive technology to compensate for their particular language difficulties. Then they can focus on the advantages of having a dyslexic brain!