I'd say have a talk with your mom first. See how she's feels on this subject. Then have a sit down with your mom and your grandparent and see what exactly the objection is and how you can work it out so everyone is happier. It'll be a good exercise for you in some valuable life skills and how to get along with people when they don't agree with you.

You might also remind your grandparent that if you are at home caring for your snakes, learning about your snakes and being online here talking with other snake owners you aren't out on the streets doing bad stuff or online at sites that some teenagers tend to want to be on too much that aren't really good for them.

Perhaps your grandfather is concerned you will keep adding more snakes. Or that they may escape. Or that they pose a health risk. Talking calmly and respectfully with him and your mom may help you address those concerns and come to an agreement. Remember respect. Even if you disagree strongly with him he is your grandfather and will not likely respond well to a smart mouth attitude (not saying you'd have one but it's easy to get overly emotional about things).

Be prepared ahead on how you want to address his concerns. If he asks something you aren't sure of, don't fake it - just respond acknowleding his point and that you will go and find the answer and come back to him with it. That sort of responsible, mature attitude is always a winner with us older folks.