If you use DatePicker control (.net Framework >= 4.0) you can bind it also directly in the XAML code like this :
<DatePicker
x:Name="datePickr"
MinWidth="150"
Margin="10"
DisplayDateEnd="{Binding Mode=OneWay, Source={x:Static
System:DateTime.Today}}"/>
and if you use DateTimePicker control from Xceed Extended WPF toolkit you can bind Maximum Property the same way as DisplayDateEnd for DatePicker.
p.s. Don't forget to add folowing to your XAML file header:
xmlns:System="clr-namespace:System;assembly=mscorlib"
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