Give a stream of consciousness and then the final answer. The Maine Coon is the largest breed of domestic cat. On average, males weigh from 13 to 18 lb (5.9 to 8.2 kg) with females weighing from 8 to 12 lb (3.6 to 5.4 kg). The height of adults can vary between 10 and 16 in (25 and 41 cm) and they can reach a length of up to 48 in (120 cm), including the tail, which can reach a length of 14 in (36 cm) and is long, tapering, and heavily furred, almost resembling a raccoon's tail. The body is solid and muscular, which is necessary for supporting their own weight, and the chest is broad. Maine Coons possess a rectangular body shape and are slow to physically mature; their full potential size is normally not reached until they are three to five years old, while other cats take about one year.

Based on this passage, how long does it take for a maine coon cat to be fully grown?
The relevant information to answer the above question is: Maine Coons possess a rectangular body shape and are slow to physically mature; their full potential size is normally not reached until they are three to five years old, while other cats take about one year.
So, the final answer is three to five years old.