Female budgie has thinning chest feathers

[BUD12]

I have an almost 3 year female budgie, and lately she has been over preening her chest feathers. They are not totally pulled off, but you can tell they are thinned out. I read on one of the posts here that females do this before they start to lay eggs, to keep the eggs warmer, is that true? I am not trying to breed.
She is in with male parakeet (2-3 months old) who we had for a little over month. Both birds are hand tamed. I need some advice what to do. I rather not seperate the birds because they are bonded and I have a small apartment so they can here each other. Please advise. Thanks

[Skybird]

laying an egg is quite possible, but doesn't mean it will be fertile for sure. i had a keet that laid eggs and ate them, and there was no male at all! i'm really not sure how old the male is when he is sexually mature. i wouldn't worry too much at this point, just keep an eye on things. best of luck!