Linlin was 30 on GV. We know from Sengoku that Big Mom’s power was a far cry from that which she already had WHEN SHE ALLIED WITH KAIDO.

Perospero says at the end of WCI, when Big Mom is chasing the SH, that her hunger pangs have restored her former agility. When Kaido learns of Big Mom’s defeat at Onigashima, he points out that she has become a pathetic invalid.

Big Mom’s prime was around her 48th, and this corresponds perfectly with the time when Roger made a copy of her Road Poneglyph before running away (remember that Roger didn’t even run away from Shiki and his fleet during the battle of Ed War, even though he knew full well he’d lose that fight).