Rise to Power
The Great Last Lord had been alive for roughly 10,000 years.
Before Demon King Earl was even born, he was already in the Furnace gathering followers to do his bidding. He grew stronger slowly compared to the Horned that he met in his time, but it was always consistent. While others had breakthroughs to get through each level, he, on the other hand, just had to bide his time.
In 8000 years, he made it to the SS rank from the F rank, and in 2000 more years he made it from the SS rank to the G rank. Though this seemed like a terrifying amount of time, every year that went by he really did have a consistent increase in power. In 500 more years, he'd likewise be in the midlevel of the G rank, and in 500 after that, he'd be in the peak of the G rank!