To be exact verbs "практиковать" and "практиковаться" have different meanings. Though all of them can be translated as "practise".

"практиковаться в чём-л." - to make exercises. And I don't feel like it is old fashioned.
"практиковать что-л." - to do smth. usually (to use smth. normally). THIS is very literal and old fashioned.
"практиковать <without object>" - to work professionally. Практикующий адвокат (врач).