The MC dies of old age and gets reborn as an orphan in Naruto, in the village hidden in the sand.
In his past life the MC was an army general who served the army for over 40 years before hel fell ill. Being bedridden without anything to do, the MC decided to watch anime and read manga to pass the time.
After his death, he meets god who gives him the chance to be reincarnated in Naruto.
The MC will be the same age as Shisui Uchiha (Shisui was 16 when he died and he would have been around 20-21 years old at the time of the Konoha Invasion)
Possible Kekkai Genkai (Google them if you don't know them.)
1. Scorch Release (Could make MC related to Pakura)
2. Swift Release
3. Shikotsiumyaku (This one is a bit of a stretch.)
4. Typhoon Release (Strong wind kekkao genkai)
Being born during the the 3rd Ninja War, the MC was forced to graduate early and was sent to participate in the war.
1 year later the war ends and he returns to Suna and starts training. During that 1 year span, the MC made a name for himself and got added to the bingo book as a B Rank ninja.
After the war ended, the MC started going on missions quickly becoming more powerful and was promoted to jonin.
However the village was still in a difficult position and the 3rd Kazekage was unstable so when Orochimaru approached the Kazkage about invading Konoha he agreed and wouldn't change his mind no matter what anyone told him.
(I dont know how you want to write the konoha invasion, you could make it so that the MC notified the Hokage of the Invasion warning him that Orochimaru killed the Kazekage and was planning to destroy konoha.)
The MC knowing that Orochimarus would kill the Kazekage wouldn't save the Kazekage because he believed it would be for the greater good.
After the Konoha Invasion, the village needed a new kage, the MC being the most powerful and respected shinobi in the village was selected as the Yondaime Kazekage.
With his experience as a leader, he will turn the village into a powerhouse.
As the kage, he will develop powerful Medic ninja, seal masters, anything that could make the village more powerful and safe.
Eventually you will have Akatsuki invade to capture Gaara.
5 Kage Summit Arc.
Then finally the War Arc.
Things to consider:
1. You want the MC to have an OP jutsu or a kekai genkai that would make him more interesting and powerful.
2. Write about the political side of leading a village, managing the village, relationships with other villages etc.