When can I start trading in Pokemon Diamond?

Can I start trading as soon as I get to a Pokemon Center, or do I need to beat the first gym leader before I can start trading? So basically what I want to know is, what is the earliest point in Pokemon Diamond when I can trade?|||you can start trading when you get to the very first Pokemon center. Then you can trade all you want but if you don't have the correct number of badges, the Pokemon will not listen to you. So you can trade at the very first Pokemon center. It just wont listen to you until you have the right amount of badges. I forget the amount of badges you need for each level of Pokemon but search it up and you will eventually find it.|||When you beat the first Gym leader. Then go to the trading center in Jublife City, in the upper left-hand quarter.|||wow people still play pokemon -.-... try a new game pokemon got old no offense