@Kai:
I don't think Sengoku used his fruit a lot because some nearby marines claim that they have never seen him use this power before the war
he didn't used anymore when he became the fleet admiral
but that sure wasn't the case when he was an active marines. is nickname is sengoku the buddha,his devil fruit is famous enough to be part of his nickname,basically is what he became famous for.
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@D.aelthasaar:
Still in the OnePiece world it's easier to see people with Akuma No Mi up to 40 years (considering how they look like) than oldies.
You can say that the pirate and marine life is hard and the life is on the line so it's hard to age and easier to die and it's true, but I hink there's more to this.
Sengoku is not older than 50-55 and so was Whitebeard (more or less).
If you think about it, Whitebeard couldn't be more than 30-32 when Roger died.
People seems older but just because everyone looks older.
For example Zoro that is like 18-20 (might be wrong, don't remember exactly) looks like a 25-30 yo man.
whitebeard was the exception.
he was considered a demon because he maintained his fame as the strongest man even in old age.We don't see old pirates because they probably retire before old age..rayleight being the prime example of a great pirate who decided to retire and live pacefully.
also,if i remember correctly..the original admirals are all over 50 years old,so sengoku (and garp) are definitely older than that,and more close to whitebeard's age,that was around 70 if i remember well