Is there a difference in dyslexia testing protocols for children (7–12 years) versus teens (13–17 years) versus adults (18–21 years)?

If by protocol, you mean what we assess and how we make a diagnosis, not necessarily. But it does require different test measures at the various ages in that some tests are only normed for certain ages. The protocol, though, involves benchmarking a person’s phonological processing and written language skills against his or her verbal comprehension skills and taking it from there. Here is a bit about assessment.

We have many tests that are normed for children, teens, and young adults. It can become more challenging to find appropriate tests for the older adult, particularly if he or she has never been assessed. The older adult has, most likely, developed compensatory strategies, and may not evidence the clinical markers of dyslexia. We can even find that situation in teenagers who have been “successful” in their earlier schooling. They evidence a pattern of strengths (in verbal comprehension) and weaknesses (in reading, spelling, and writing), but the weak areas fall in the low average range, not the clinically disordered range. Here it takes an accomplished diagnostician to interpret both the test scores (quantitative data) AND the qualitative data when making a diagnosis.