My Lovebirds are breeding way too early!?

I bought a pair lovebirds in mid Sept. of this year, a Peach faced (male) and a Dutch blue (female) they were both 4 months old . I have them in a good sized cage with water, food, and toys (NO NEST BOX). When i had just bought them they would fight a lot, but now they seem to have settled down. Yesterday i was cleaning out my other cages when suddenly the hen went towards the bottom of the cage and then shortly after the male joined her... then mating started, i watched them mate for about 2 minutes and then they were at it again later that same evening. Personally i think this is too young for them to be mating. Can anyone explain this? What should i do, should i give them a nest box? Please i am asking if anyone out there can give me some advice on this. Thank you