Here I go again...well since agabomba asked me I kind of started on this but there was no point in half assing it so here goes. I will make updates to this later on.
No way Yahiko was much younger when he died they where all still kids more or less about 16-18. Though I know it was mentioned by one of the Leaf ninja that Pain's God realm looked to be in his mid 30's which seems odd knowing his a corpse.
It must mean that Nagato was able to grow/age Yahiko's dead body. Which kind of makes sense if you think about it because if Pains where all corpses their bodies would rot and look like zombies. I think the Pain bodies do age but this is slowed down by Nagato's Revive/Repair jutsu.
So to put it in a time line roughly speaking
*Time line is based on present time and going back
* "?" means the age is estimated but is unknown.
-63 Years: Hashirama(28?) & Madara(28?) create the Leaf village // (Tobirama 25?), (Toka Senju 27)// (Sarutobi 8)
1st Tsuchikage explains to Onooki (10) about the Rock symbol of the Earth village
-62 Years: Hashirama(29?) becomes the 1st Hokage
The Cloud village tries to capture the Kyuubi but the Gold & Silver brothers get swallowed
Sarutobi(9), Homura(9), Koharu(9) become Tobirama's(26?) students
-61 Years: Madara(30?) Confronts Oonoki(12?) & Muu(??)
Madara(30) leaves the Leaf village
1st Great Shinobi War begins
Kakuza(30) of the Waterfall village attempts to assassinate Hashirama(30) and fails
-60 Years: Hashirama(31?) and Madara(31?) battle at the Valley Of End // Tobirama(28?),
-56 Years: The Cloud's 2nd Raikage attempts to sign an alliance with the Leaf's 2nd Hokage but they get attack by the Gold & Silver brothers. The 2nd Hokage(32?) nearly dies
-54 Years: 2nd Hokage(34?) sacrifices himself and makes Hiruzen Sarutobi(17) the 3rd Hokage
Jiraya, Orochimaru & Tsuande are born
-50 Years: 1st Great Ninja War ends (Sarutobi 21)
-48 Years: Jiraya(6), Orochimaru(6), Tsunade(6) graduate the ninja academy and become Sarutobi's(23) apprentices
-37 Years: 2nd Great Ninja War begins
Jiriaya(17) Gets his prophecy from the Great Frog Sage and begins to wander
-36 Years: Tsuande's(18) brother Nawaki (12) dies
Jiraya(18) returns to the Leaf
-30 Years: Jiraya(24), Orchimaru(24) & Tsuande(24) battles Hanzou (32?) // (Sarutobi is 41)
Jiraya(24) decides to train Yahiko(9) , Konan(9), Nagato(9)
Motoi's(5) father is Killed by the 8 tails Ay(18?) slices off it horn & Killer B(5) is selected as the next host of the 8 tails
-28 Years: Sasori(7) becomes graduates Academy
-27 Years: After 3 years training Yahiko(12) , Konan(12), Nagato(12), Jiraya(27) then returns to the Leaf // ( Sarutobi 44)
Tsunade's lover Dan Kato(27) dies
Minato(10?) graduates the Ninja Academy and becomes Jiraiya's(27) apprentice
Sasori(8) becomes a Chunnin
-26 Years: Minato(11) rescues Kushina(11) from Cloud ninja
2nd Great Ninja War ends
-25 Year: Kakashi(5) Graduates the Academy
-24 Year: Kakashi(6) becomes Chunnin
-23 Year: Gai(7) graduates the Academy
-22 Years: 3rd Great Ninja War Begins
Shizune(9) Graduates the Academy and becomes Tsuande's(32) Apprentice
Kurenai(9), Asuma(9) Graduate the Academy
Kisame(10) Graduates the Academy
-21 Years: Yahiko(18), Konan(18), Nagato(18) Akatsuki gets betrayed by Hanzou(41?) and Yahiko dies.
Ibiki(10) Graduates the Academy
-20 Years: Sasori(15) kills the 3rd Kazekage and leaves the Sand. Shortly after the Sand gets attacks by presumably the Earth village.
Tobi arrives in the Mist and influences Yagura(15?) 4th Mizukage
Yamato(6) graduates the academy and becomes a Chunnin the same year
Zabuza(9) graduates the academy
-19 Years: Asuma(12), Gai(11) become a Chunnin
Kabuto(4) is found by Mother (Nono) and joins the Orphanage
-18 Years: Shizune(13), Kuernai(13) becomes a Chunnin
-17 Years: Kakashi(13) heads off on his first mission as a Jounin with Obito(13) , Rin(13) & Minato(20?)
Ay(31?) & Killer B(18) face off against Minato(20)
Danzou's(54) Root entourage including Orochimaru(37) and another Unknown meet with the Agent "The Walking Maiden (Nono)" and Kabuto(6) joins the Leaf and becomes a spy.
Anko(10) Graduates the Academy and becomes Orochimaru's(37) apprentice
3rd Ninja War ends
Sarutobi(54) discovers Orchimaru's(37) lab and he escapes the village
Minato becomes the 4th Hokage
Jiraiya(37) leaves the village to track Orochimau
-16 Years: Kyuubi attacks Leaf village and Minato(21?) & Kushina(21?) die. // (Sannin 38) (Sarutobi 55)
(Fugaku 32), (Mikoto 27), (Chouza 22), (Shikaku 25), (Inouchi 22), (Shibi 23) , (Kakashi 14), (Gai 14), (Asuma 15), (Kurenai 15), (Itachi 5)
Ibiki(15) becomes Chuunin
-14 Year: Itachi(7) Graduates Academy
-13 Year: Itachi(8) masters Sharingan
-12 Years: Kisame(19) kills Fuguki Suikazan and takes the Samehada then meets Tobi
Kabuto(11) is nearly exposed while spying undercover on Iwagakure and he accidently kills Nono who doesn't recognize him.
-11 Years: Itachi(10) becomes a Chunnin
-10 Years: During peace negotiations the Cloud tries to kidnap Hinata & Hizashi is sacrificed
Kisame(21) leaves the Mist village
Very likely Yagura(25?) was discovered to be under Genjutsu and had the 3 tails extracted.
-9 Years: Mei Terumi(25?) becomes the 5th Mizukage
Zabuza(20) meets Haku(9) and leaves the Mist and becomes a mercenary.
-8 Years: Itachi(13) becomes an ANBU Captain
Shisui(19?) commits suicide and gives his eye to Itachi.
Itachi carries out the Uchiha clan massacre then leaves and Joins Akatsuki
Orchimaru(46) leaves Akatsuki
*Hanzou's age is just a rough guess
*This means roughly speaking Minato is about the same age group as Chouza, Shibi, Inochi and Shikaku and would be about 37 if alive today.
*The hard part is nailing Minato's age but I think he was fairly young
The exact end date of the 1st ninja war is a really rough guess but the 2nd and 3rd can be more easily estimated from details in he story.
Interesting note about the ninja wars: (based on my estimates)
1st Ninja War = Lasted 13 Years
13 years of Peace
2nd Ninja War = Lasted 11 years
4 years of peace
3rd Ninja war = Lasted 5 years
17 years of peace
4th Ninja War
What you will notice is that while the 1st and 2nd Ninja wars where longer than the 3rd the real big difference is the amount of peace in between. There was a fairly decent era of peace between the 1st and 2nd ninja War where the villages had plenty of time to recuperate their losses.
However the 2nd Ninja war was probably one of the most brutal which is why so many of Tsuandes classmates died as well as being the longest war. The gap between the 2nd and 3rd Ninja war was very short thats why at the beginning of Kakashi Gaiden it mentioned that the Leaf was suffering from severe lack of shinobi. There was not enough time for the villages to recoup their losses so the 3rd Ninja war ended quickly.