question about dwarf puffers

i recently got a male and female dwarf puffer, i've never had them b4. i had a gsp but he was sick when we got him (a different girl that worked there told us a week after we got him). but from what i've read these little guys are fish killer for sure! I have them in my 30g tank with neons, tetra, swords, and other fish like that. These guys are small, the male maybe a bit over 1cm and the female no bigger then 1 cm. Now my question is how old are they before they get really aggresive? They haven't bothered anybody else yet, been there for a week i think. The female pretty much stays in a low bushy type plant we have and the male explores but doesn't seem to care about the other fish. They sometimes swim together but not always. There's lots of plants and a huge piece of drifwood in the tank. Also some bigger rocks. How long do you think it will be before I have to have their own tank ready? And maybe life span of these guys and breeding tips, just for info, no real plans.