My bettas ate goldfish flakes occasionally when I was out of betta pellets, so I wouldn't think tropical fish flakes would harm them one bit. 

Regarding the time span it takes for a goldfish to reach sexual maturity, it varies from fish to fish.  As soon as a male goldfish sports breeding tubercles on it's gills and pectoral fins, it is able to breed I know.

Fantailer- I've been reading a lot about breeding lately too. Most sources say you should wait until the fish is at least two (if they're mature then) so that you can spot any problems that may be genetic and see their adult color. Who are you thinking about breeding? I am only going to try with Rowan and Aspen since they are show-quality, from a breeder. I'm waiting til spring after next.

Oh I see. Well that's good then! I don't think it's something that should be taken lightly. Perhaps by keeping the tank a constant temp throught the year you could avoid it...dunno. Or just separate them I suppose.

If the tank is heavily planted and the fish is well fed it's quite possible for some to survive, I have read several instances on here. But from what I've read it usually takes a bit of interference to ensure breeding, live food, change in water temp, increased aeration, etc. and as Skwishkee said that even in the unlikely event they do breed the eggs/fry probably won't survive. They require a special food and filter. So not to worry.

If I had eggs in my goldfish tank, I'd definitely separate them into my quarantine tank!
Besides, I bet a pet shop would be happy to take care of some small goldfish babies later! It would be very time consuming to bring the kids up though, so I probably would get so attached to them I'd just give them to friends and family <3

...but I had planned that Berry and Atlas would breed :'C I always thought Berry would make a great mother considering how attached Baby got to her <3