I can't tell you how much of a similar situation I'm in. I've been practicing for about 2 years, yet I can't muster up the courage to mention a peep to my dad. He's a man with STRONG Christian morals. He believes, "If you don't believe in God, you're going to hell with Satan." Exciting, isn't it? :P
Now, mothers are usually more understanding, yet they can become just as confused. My mother, who was Catholic, passed away 16 years ago. I remember last year, I attended a Samhain ritual and we did a meditation to reconnect with loved ones. The images I saw were my mother playing with my Boston Terrier, Buttercup, who past away last July. She looked at me and smiled before Buttercup came over and wagged her tail. I felt the tears falling down my cheeks when I finally told her I was Wiccan. She continued smiling and said, "It's okay, sweetie. I still love you." We embraced tightly and I cried on her shoulders.
She still accepts me, but she can't tell me dad, since he's still alive. I'm going to be 18 soon, so I'm hoping that if he ever finds out, he will understand.
Now, age-wise, there is no specific age you need to be to practice Wicca. I know friends with children that are already practicing in their rituals. However, in our cases, that would be impossible. What I do in order to attend rituals is take the bus to each one. It's tedious, but it's what I always do. If my dad asks where I went, I tell him it's a gathering with friends, which is technically true. If your mother is that suspicious with that same excuse, don't panic. If you manage to find a group in your area, e-mail them and tell them your situation. They can surely help you. Other than that, keep doing your research and if you really want to wait until you're older, do so. It's all up to you.