Well, the real point that should be made is that fighting isn't the main worry in putting a male and a female together, it is the constant stress on the female of the male trying to mate with her. Mating and eggs are a huge stress on the female and if the male is kept with only one female all of his attentions are on her and you will find her life span is vastly shortened. I know this may be hard to understand since you haven't seen it yet after only 2 years, but she's not going to live very long. Some keepers here can vouch they see this even when they have multiple females with a male. It is really better just to keep separate all sexes of leos you don't intend to breed and those you do, introduce only as necessary.
If you introduce a smaller animal to an established colony you will find the smaller one getting weaker and weaker, this is very common across all species. In fact, you can and may see males eat other babies, especially if they are not their own genetics. (Another very common occurrence over most animals) Survival of the fittest. The biggest and strongest eat first, eat best, grow more.
Also take into consideration food and feeding. Even if the younger got its fair share, how are you controlling the size of the prey it is eating? How do you monitor its intake and fecals?
I doubt you will find someone to tell you that it has been done here. Plainly and simply because it is not a good idea in any way. If you really want another gecko, grab a 10 gallon, wait 9 months, get everyone the same size and then see if everyone gets along. Besides the fact you want to keep the new one isolated in quarantine for a few months anyways before introducing it to any of your other geckos, just for safety's sake, you may as well wait until it is older.
Hope this explains better.
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0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock