this happend after not before so its Shanks overwhelming presence that stopped him

Ehm no both have the same source there function is different but source is the same again a basic you didnt understand if you didnt learn the alphabet its hard to discuss you know because of obvious reasons ?
DF doesnt grow old but the user him having haki its true its a long range attack and its not really concentrated his fruit destroys the whole area also attacks like that are easy for Logia users