i wanna put my 2 cents into the last few post since i haven't posted since xmas.
(warning long post skip if ure not into readin alot lol )

The ages of kakashi becoming a jounin and itachi becoming a jounin shouldn't go into consideration when talking about skill nor the activation of sharingan between itachi/sasuke/obito. The main reason is all of these people were brought up in diffrent times. Kakashi was brought up in a time of war of course there ninja would have more experience in battle because they maybe have been forced into nijna fights instead of finding a pet for someone (IE:team 7's first few missions finding pets/cleaning garbage) I doubt the village took such jobs during war time.

If im not mistaken the viallge was in a peaceful time (none war) when itachi was around so he may have been a genius but maybe the village wasn't pushing it's ninjas as hard to move forward as chunin/jounin, if he killed the whole clan he would have to be powerful at a young age i doubt he just gained a huge ass power boost when he became 12 out of no where.. He still faced danger at an early age to gain the sharingan though so he was most likely in some high lvl missions at an early age. which comes to the sharigan being obtained and what ages has to do with it which is.....nothing. It is activated when a uchiha is in danger or pushed to the limit, look how obito and sasuke gained it they where both in mortal danger. Sasuke can't control when he would be placed in a real mission to even experience battle and gain the sharigan.

Ok with the strongest 5 ninjas in the village i would have to go with...
1.4th hokage: he created some of the strongest justsu's we have seen, he defeated the kyubbi in a sense, and as we saw in kakashi gaiden he was feared and could take out large groups of ninja easily by himself.

2. 1st hokage/madara: im placing them together because they were the founders of the village, both having very powerful bloodlines and madara had mangekyou. even with that the first beat him. but i keep them together cause madara is still alive some how.

3. 3rd hokage: yes he died without killing oro i understand that, but oro even said it if he was 10 years younger before that fight he would have won old age played a big part in that battle. He knew all jutsu in the viallage need i say more.

4. Itachi: He smacked around kakashi an oro i can't place either of them ahead of him and oro ranks up with the rest of the sanin so i can't put jiraya here either. yes i know he ran from jiraya but he was already weakened from using MS multiple times in a short period. Also he took out the whole uchiha clan and second person to activate MS ever.

5. oro/jiraya: im placing them together cause i believe they are both stronger then tsunade (all we've seen from her is strenth/healing capabilities) but we never seen them against each other at full stregth against each other to choose who is stronger. Both have many jutsu's, the both where under consideration to become hokage at one point.

Well thats my opinion we are all intitled to one, I can't place kakashi up here nor the 2nd hokage (we never really seen him in action nor recieved much info on him). Kakashi could not beat itachi, he stated himself during the chunin exam that he couldn't beat oro (not sure now but we will never find out sadly) and his stamina is horrible when using sharingan since it is not his own (reason why is stamina is low sharingan eats more of his chakra then an uchiha using sharingan).