Will my lab ever calm down? and questions about labs!?

i have a 5 month old black lab (from pure english lines) he is very energetic and i take him on 2 30 minute walks a day, is that good enough? i am starting him in agility in about a week and i was wondering if he would ever calm down. he is always chasing the cat, how do i stop that? he doesnt like it when other dogs bark, is this normal? he eats EVERYTHING in sight. and he digs HUGE holes in my backyard. please help!!! thanks