Old developers can easily get set in their ways especially if they work in one environment for a dozen years or more. So how do you overcome the “that is the way it has always been done” mentality that sets in?
The first thing you have to do is be patient. Don’t try to force them to change all at once. Too much change at one time can be a shock to anyone’s system. Gradually introduce new ideas and new techniques.
The next thing you need to do is to make sure that you demonstrate examples and explain how the changes will benefit them in their daily work. One of the main resistance points is that people don’t understand why change is needed. If they can see the payoff they can more easily make the transition.
The most important thing you can do though is get management’s support. This does a couple of things. First it gives you a fall back when you encounter resistance. Secondly it relieves the existing developers of the mental responsibility for old habits. They are just doing what is expected of them.
Even with all this said thing aren’t likely to be smooth sailing, but at least you will have a fighting chance.