[Macbrother]

It's the way around, he was the God of the Shinobi because he was the strongest.
That's not a circular logic, you just didn't understand the point.

They were the strongest, so much that they remains the strongest even when they're old.
And not : oh I'm old! Now I'm strong!

Your point is to say that the oldest are the strongest, heck you take as example the strongest ninjas ever to begin with.
There are no other old ninja? Wonder why.
Because they're dead or in retirement.

Yeah Sarutobi was stronger when he was younger, Oro remains young precisely not to become weaker and finally die because of oldness, Tsunade uses Ninjutsu to change her body.
Only Jiraiya has the body of his age and guess what? Yeah he was probably stronger when he was in his prime.

You didn't say it the other way around. You answered why the sannin are so powerful at 50 with "because they are the legendary sannin." That does not answer the question of why they are able to maintain enormous chakra and ability at such an age. Your claim that they are strong now because they were stronger then is a load of crap, shinobi don't reach 25 and say "ok, I'm at my prime, now I'm going to stop learning new and more powerful jutsu because I'm at my prime." The strength of a shinobi is a continual process which depends on what their stamina, what jutsu they know, and other physical abilities. While the speed and strength may decline, the chakra remains relatively constant and the knowledge of jutsu increases.

Shinobi are bound by their physical condiction as anybody else, jutsu needs chakra, chakra needs physical condition.
And yeah there isn't only physical condition, neither for athletes.

Raikage you talk about martial artists, martial artists are athlete.
That's not because it's the JO that athlete only means doped guys running like hell.
Sharper intellect with age? Since when?
And once again you can only take the example of the strongest ninja ever in their old against young but far weaker Ninjas to begin with.

lol Jacky Chan can probably beat the hell out of you even if he's over his 50, it's not because he's old because he was even better when he was young.
It's just that he's far stronger than you are period.

You are continually missing the point. Ninja abilities are bound by much more than their physical ability alone, that being their intellect and jutsu knowledge. They are in a sense part-athlete, part-martial artist and part-spell caster. It takes no physical speed or strength to sit back and move my hands really fast and overwhelm a younger, healthier shinobi who doesn't have the jutsu to compete.

Let's say a shinobi john learns Katon super fireball at 25, then learns Katon grand fireball at 35, then learns Katon ultimate fireball at 45. John is strongest at 45, why? Because he has learned better and more capable jutsu, regardless of his waning physical strength and speed. His chakra is remaining reasonably constant because the increase in his traning and experience are balancing out the decrease his physical energy. That seems to me a reasonable explanation as to why sannin retain their enormous chakras even at 50. Yes, this example is contrived but the point remains, time allows for learning and creation of better jutsu which can make a better shinobi, period.

Firstly how do you know that Oro didn't know the Edo Tensei when he was 25?
Then I don't know how would be the body of Oro in his 50 so there is no point in that and finally, you take the example of a Ninjutsu freak.
I will do the opposite : Gai will be better at 50 than at 25 when he will be weaker and slower?

Because that's ridiculously unlikely. To create and master such a jutsu he would've surely needed test subjects (sacrifices) along with a huge amount of time; anbu and chuunin weren't disappearing until shortly before he left (at 35+?) and he was still doing missions for the village and such. It's much more likely he learned this in his later years, along with his immortality jutsu after and during the time he fled the village, where he could work on it alone, in private, and with as many randomm people he liked.

Don't try to evade the question either, it's painfully obvious the Orochimaru of now would lay waste to the Orochimaru of 25, his shit would no doubt be in ruins, he no doubt has a much more vast arsenal of ninjutsu than he did at 25. As for Gai, that's a good question. Maybe, maybe not. That depends on what taijutsu techniques he could've picked up in those 25 years. Taijutsu is the arena most dependent on physical strength and speed so he may or may not be able to defeat a younger Gai, again, depending on what if any new taijutsu abilities he learned.

Actually that's not what Oro said, he said that 10 years younger, the 3rd could have probably been able to kill him when he had enough strength to pull out his soul.

Sarutobi could stand up against Oro 13~15 years old ago during their first confrontation.
It appears that Sarutobi isn't the God of the Shinobi for nothing.

Whether he was referring to that specific technique or that he could kill Oro overall 10 years ago, we don't know, but it's irrelavent. Let's just replace 10 with 13, not like it matters. So at 54 he could've still defeated him, my point remains.

25 years old isn't young for ninja fighting since they're children.
Kakashi is obviously known internationally as Copy Ninja Kakashi.
The Sannin were legendary in their 20, Itachi became (in)famous at 13 when he whipped out his clan.
It's also about this age that the 4th saved Konoha from the Kyubi.
They become Ninja at 6~12 years old, their job is the deadliest.
No 25 years isn't young.

Especially for the 3rd and the Sannin who lived in a era of perpetual war.

It's young compared to 50. Yes, the sannin were legendary when they were in their twenties, as was Yondaime. Again, we're not talking about 'legendary' so bringing up the sannin, are meaningless. We're talking about "best of all time", that's a step up from legendary, you agree? Good, now, the point is, was he called "best of all time" at 25, and I think that's pretty unlikely.

Actually that's pretty much exactly what you said, a little quote?

The point of me using Sarutobi was that we are not just talking about legendary, we are talking about "best of all time." Yondaime did not have the time Sarutobi did to build up that kind of legend, which is what I said.

So that's excatly what I said, there is no 'probable' in your point, it's just your wish.
Yeah the 4th has enough time to built his legend, and he became the greatest hero of Konoha by saving all the village from the Kyubi.
Still he's known as the strongest one.

Right, so creating the arguably the most powerful jutsu in existance, creating the Rasengan, along with overcoming Kyuubi all at the "young" age of 25 doesn't lend any credence to the fact that Yondaime "probably" would've been the greatest of all time had he more time to create new jutsu and tackle more problems. Uh huh.