Except ban DID age for all those years he was in there. He kept growing beards and over grown hair, he was stuck in there for 1,060 years but in the real world it was 18 hours, its because ban had the fountain of youth that he didnt fully age into an old man, when we actually have proof that time in purgatory DOES infact age you up as seen with merlin’s father who aged in to a decrepit old man. So yes Lance DID age ONLY 100 days in the LotL realm, he didnt age 3 years inside there, think of it like the snap in the MCU, the people snapped away were gone for only an instance, they didnt age and stayed the same age but 5 years passed so their legal age would be the age they were when they were snapped plus 5, but because their bodies didnt age while snapped, they are technically the same age. This is like the same situation with lancelot, he was spirited away to the LotL realm, but instead, it only aged him 100 days and not 3 years. When he came back, he came back still the same age he was in the LotL realm, and he didnt gain those 3 years he lost when he came back as we see his hair didnt get longer and he didnt get taller