Pigeon blood types, such as the yellow marlboros, typically mature around 12 - 14 months. Males usually take 3 months longer than females to reach sexual maturity. Non-pigeon types typically take 3 months longer. Blue diamonds, in my experience, can take 2 full years to reach sexual maturity.
At an early age, discus often display pre-sexual behavior - sorta like puppy love. It's very common.
Willie