You'll need to call Marriott Rewards customer service for your lifetime points total. It's not available in your online account data. They are very nice when called and can hook you up quickly. You should have a phone number on the back of your card.
The lifetime points and nights needed for Lifetime Gold are, 1,600,000 points and 500 nights. Platinum is 2,000,000 pts and 750 nights. You've blown by Silver if you have 1,200,000 points and 250 nights.