34 male, ekg, echo stress fine. out of shape. throat burn after walking. is walking enough cardio at my age? can i start by walking for 30 min/day?

Exercise: Starting by walking 30min/day is excellent, work up to 3mi/day and then work for 3mi in less than an hour say target 3mi in 45min every day. At that point it should have taken you probably 6 weeks or perhaps more to get there and you should notice a good improvement. From there you can discuss with your Doc if you want to push to higher work loads.