The above 2 answers are right on.
There's nothing wrong with them using the heater except that I've experienced the eggs dying from the extra heat created by the heater. If I were to leave the pair where they are, I'd put some slate or other flat slab in front of the heater so they couldn't use it.
If you are truly interested in having the fry survive, you be better off putting the pair in a separate tank by themselves as suggested. There are breeding stands for sale or I've used any thin, flat slate or shale rock positioned about 45 degrees between the bottom and side walls. I've used these because they were easier to handle when removing the spawns and didn't take up as much room since I was using smaller tanks.
As for the age difference, it doesn't really matter. What is typical of a young or first time breeder is that they usually have poor spawns the first few times. But the behavior you are describing seems not from inexperience but from desperation which is not a good thing. Being alone should solve this problem. Otherwise, your other fish will be getting a nice high protein (high cholesterol
) snack about every couple of weeks or so.
If you'd like more help with this, feel free to PM me. Angelfish were my specialty