Think about this, a chair is a chair if you hang it upside down. A cat is a cat if you draw it facing the left or right. A b is a q if you change its page orientation, and writing lower case letters is the first time this matters in life. It is a huge developmenat concept, and if I get this right, he is not even in Kindergarten yet, and reversals will still be nothing to worry about through first grade. Additionally, reversals have nothing to do with dylexia. Reversals that continue beyond a typical developmental stage can be a sign of comorbid visual motor and visual perceptual issues (very frequently associated with ADHD.)
Dyslexia is an inabilty to decode sound symbol relationships. He is too young to diagnose this because he is too young to have had, and understood, whole langauge reading instruction (the way most schools teach reading.) About 10% of children cannot learn sound symbol relationships and decoding without direct alphabet phonics instruction, and are dyslexic. All children can learn to read with an alphabet phonics instruction program, so if he has trouble learning to read, once it is actually time to do so, request that he be tought to read with an alphabet phonics program at the first opportunity.
As for ADHD, you do not describe ADHD issues, as activity is really not the biggest issue most children have, but it is a myth that a qualified developmental pediatrician could not diagnose ADHD this early, or earlier, with a full scale evaluation. Brain dysfunction does not kick in when children reach a certain age, it is either there, or not.
Sometimes, trying to get ahead of the curve on learning, really sets kids behind, when we do something out of order, or teach them something that must be relearned correctly later. It is one reason that kids don't really need much more than home enrichment before kindergarten begins, with parents reading to kids, talking, and singing to them all day is enough for them to excell in Kindergarten once they get there.
He has a chance of having these issues, a greater chance than most children, becuase his father has them. You should keep an eye on it, not becuse of the reasons you stated, but for signs of fine motor and perceptual issues (once he gets there) that are associated with the frequently comorbid ADHD issues, which can also stand alone if there is a family history. Bottom line though, he has to get to a point where he is beyond that developmental stage for you to see issues.
M.