As you know from previous installments (Part 1, Part 2), Lumpy the dragon was a kindhearted soul, quite different your run-of-the-mill dragon. While most dragons hoarded treasure and stole princesses, Lumpy preferred gentler pastimes like watching bees collect nectar or playing with his friend the boy.
However, Lumpy remained like the other dragons in one important respect: Like the other dragons, Lumpy lived practically forever. By the time he met the boy originally, he was hundreds of years old, with every expectation of living for hundreds more years. So his entire time with the boy was an eye-blink to Lumpy, while to the boy it stretched on for most of his memory.