I was doing some mapping for other thread.
But found this.
First , Shanks came back to HolyLand once and then returned to the lower realm , Confirmed by Shamrock.
Now in the luffy flashback , Shanks is not carrying the sword " Grpyhon ".
Gryphon looks like this.
Shanks Sword during Luffy flashback , looks very similar to Roger/Rayleigh Sword.
Now , looking at the timeline.
27 years old Shanks - When he lost his hand.
33 year old Shanks - He beat Loki
33 year old Shanks - Became Yonkou
Currently - 39 years old.
Maybe shanks went to Holy land between the age of 27~33.
Where both him and Shamrock got their respective Swords - " Cereberus " and " Grpyhon ".
Also this comment from oda ,
His sword name is " Gryphon " but how does he actually fight? ....
- Shanks doesn't fight like a Conventional Swordsman anymore.
- Shanks is stated not to loose his "power" not his " Skills " when he lost the hand.
- Mihawk disinterest in Shanks , Because he ain't fighting like he used to.
But found this.
First , Shanks came back to HolyLand once and then returned to the lower realm , Confirmed by Shamrock.

Now in the luffy flashback , Shanks is not carrying the sword " Grpyhon ".

Gryphon looks like this.

Shanks Sword during Luffy flashback , looks very similar to Roger/Rayleigh Sword.

Now , looking at the timeline.
27 years old Shanks - When he lost his hand.
33 year old Shanks - He beat Loki
33 year old Shanks - Became Yonkou
Currently - 39 years old.
Maybe shanks went to Holy land between the age of 27~33.
Where both him and Shamrock got their respective Swords - " Cereberus " and " Grpyhon ".
Also this comment from oda ,
His sword name is " Gryphon " but how does he actually fight? ....
- Shanks doesn't fight like a Conventional Swordsman anymore.
- Shanks is stated not to loose his "power" not his " Skills " when he lost the hand.
- Mihawk disinterest in Shanks , Because he ain't fighting like he used to.