When it comes to sunscreen safety, sunscreen really shouldn't be used for longer than a year. So, if I were you, I'd buy a new bottle just to play it safe.
When you're shopping for sunscreen, remember to look for "broad spectrum coverage". What that means is the it blocks against UVA and UVB rays to provide complete coverage. Blue Lizard sunscreen is a great option for you to buy. (compare prices) Pick up at least an SPF 15 (more if you burn easily) and don't forget to apply at least every 2 hours; more if you are in the water.
Pick up a couple bottles to have on hand. I always keep on at my house, one to grab when we head out, and even a small refillable bottle in my handbag. How many times do you make a detour to hang out with your friends in the sun. If you're prepared, you'll never have to experience the pain of a sunburn.
Protection against the sun is completely in your hands. One sunburn is all it takes to increase your chances of skin cancer, so make sure you play it safe before you have fun in the sun.