When we talk about acquiring skills, the construction is 'learn to + infinitive'. So, in theory, the question should be "Well, what do you think the best age to learn to drive is?". This is correct, but rather clumsy-sounding. It would be less awkward to say: "Well, what do you think is the best age to learn to drive?" This doesn't follow the rule of embedded questions, but it does sound better.

Well, what do you think is the best age to learn how to drive?

What is the best age to learn to drive in your opinion? Or what do you think the best age to learn to drive is?

I'd structure the sentence differently to avoid, what seems to me, the awkward "is" at the end. "At what age should I learn to drive?"