DD2 is about 27 months and is exactly the same!!!! We've had to be "big meanies" for almost a month to make any headway with her. It is age, but like others said still needs to be addressed. Some things we do:
1) Try not to say No unless we mean You seriously better stop that right this second or else, so she knows its serious.
2) If we say stop and she doesn't, we take it away. Oh the hysterical screaming! But its all that works, and after doing it for awhile now see can say Stop or I'll take it away and it works.
3) Choices choices choices: pick your pajamas or mommy will, do you want to walk to bed or daddy carry you
4) Keep discipline explanations short and simple: You are in time out for hitting mommy, hitting hurts. The more you talk about it the less they listen.
5) Find some way to get a break for your own sanity. Maybe daycare one day a week or something, its SO refreshing!!
Its a rough age, especially with a strong willed LO. I feel like a failure with mine at least once a day!!