Enable/disable form controls (Active method)

1).From controls
purchline_Assettagno_ss3.enabled(false);
purchline_Assettagno_ss3.enabled(true);
2). we Can enable/disable buttons also write in initvalue/active method
if(cust.age>20)
{
Button .enabled(false);
}
else
{
Button.enabled(true);
}