Gifted Issues Discussion homepage Forums Identification, Testing & Assessment At what age is a LD likely to be found?

Doubtful, at least not enough to make the achievement discrepancies insignificant. It's more likely that something is interfering with his acquisition of academic skills--aka a learning disability of some kind.
I assume OIO is where he reached a premature ceiling?
This verbal memory score concerns me, falling as it does at the lower end of the Average range, especially with those high VIX scores. I'm always on the alert for memory and processing speed issues in dyslexia/dysgraphia situations.
Again, auditory-verbal memory scores have relative vulnerabilities in them (memory for words (short-term), retrieval fluency (long-term)). Also, now we see processing speed relative concerns, especially with symbols (visual matching). Interestingly, decision speed, which uses pictures of common objects, is a strength.

The nonverbal/visual area is a bit of a mixed bag over the two tests (RIAS and WJ), with a good score in attention to visual detail of concrete images, and average-to-unclear results in spatial and reasoning areas.
Oral language achievement approaches the level found on the RIAS VIX, which suggests that the verbal cognitive ability is grossly accurate.
Reading achievement is far below levels predicted either by the RIAS VIX or by the WJ OL achievement. Notably, the speeded, fine-motor involved aspect of reading was untestable, and reading comprehension was even further below expectations than word calling. (Keep in mind that a typical five year old is not expected to have much reading comprehension at all, so a low average result in this area in a child with this level of verbal cognition is quite striking.) Also, at this level, almost all of the words read are sight/high-frequency words, or simple cvc words, so minimal draw on sophisticated phonological awareness or phonics skills is needed.
Same thing happens in the remainder of academic achievement. Untimed skills are slightly low-to-approaching appropriate for this cognitive ability, and timed, fine-motor-involved tasks are untestable.
Rhyming appears age-appropriate overall, but there is a 23 point difference between ability to produce rhymes and ability to hear rhymes.
Overall, did adequately on this level of phonological awareness, but still well below verbal ability in several areas, especially rhyming, segmenting, and substitution.
Fine-motor definitely looks like a relative weakness, in the bottom of the average range, well below verbal cognition, and even aspects of nonverbal/perceptual cognition.

I would be investigating reading and writing disabilities (dyslexic/dysgraphic), with the related cognitive processing areas mainly visual-spatial reasoning, language processing/memory, processing speed, and fine-motor/visual-motor integration. I would consider speech and language eval (especially for language memory, retrieval fluency, and auditory discrimination), and definitely include OT.

While the process is winding its way, do lots of read-aloud, with him narrating back to you, to maintain intellectual stimulation and access to higher-level vocabulary, as well as to exercise auditory working memory. And scribe any written response longer than a word or two.