I would have the battery tested, it may not be the cause of your starting issues. My OEM battery lasted 5 years; going a little over 3 on Bosch replacement. 4 years isn't out of range for normal, but have it tested. Your location will also impact battery life, ie, if it's very cold there, battery life is shorter.
FWIW, I've always had terrible experiences with Optima. I never got more than about 1.5 years from one (blew through 3 Red Tops). Advantage of a yellow top is if you run electronics with the car off, they are deep cycle. It doesn't really last longer than regular battery or start better than standard battery or red top. I only ran Optimas because I had relocated my battery to the trunk and didn't want to install a vent tube - Optimas are sealed.