I think your concerns are very valid. 4.5 years is not too young, especially if he has energy to burn and as long as he is not pushed too hard to achieve. You seem very concerned about it anyway so I think you will be good at not making it a chore for him.
However, the ADHD problem needs to be addressed with a doctor and or advice from someone who has been through it. My child is on ADD medicine ( He is not Hyper and does not need Ritalyn, he takes Aderall) I had many concerns about "drugging" my kid but in the long run I could'nt let him fail his grade or be put into special classes because I refused to see a doctor. My son has more focus on wrestling, Football, Baseball and especially school work than ever before. He does not walk around like a zombie nor is he "addicted" He does not take the medicine in the summer nor on weekends and he has absolutely no problem with "withdrawls". As a matter of fact he does not notice one way or the other. I, however, and teachers have seen vast improvements. I also think you'll find many more kids that have dropped out of school and got addicted to drugs due to the fact they didn't take medicine and really needed it. I do think though that my situation is different because my kid is already in slo mo without drugs. Being a mother that has a child with ADD I've talked with and been around many others who are on these medications and to my knowledge those who do need it and take ridalyn are not completely altered and are not zombie like. One more thing, It took me over a year to get him diagnosed and taking medications. We saw three physicians, a psychologist and had many many conferences with teachers and councelors. It's not as easy as everyone thinks. My son used to get all D's and F's (except gym) and now he is maintaining a B average. These are not magical pills and we still have to work hard on homework and everything else but if I hadn't of decided that what the teachers had been telling me for three years was symptoms of ADD I could have let my son fall even further behind.
Anyway, thanks for letting me voice my opinion.