Hi Imran, I will try to answer questions if I can.
1. If the iris is yellow he might be a little older than 12 months, my grey is 13+ months and hers are more cream color, sounds more like a 2 year old or older.
2. Untill he gets used to you he won't eat from your hand, give it a little time, it will happen.
3. You need to get him off the sunflower seeds as a regular diet, they are ok for a treat but he needs a good quality pellet and a variety of vegetables and fruits. This will have to be a gradual process and I think we already have a thread that deals with that.
4. This is normal to puff up, he is not used to you yet, it takes time to form a bond and for him to trust you so go slow and it will happen in time, don't push for more before he is ready.
5. It is perfectly normal for them to be climbing all over the cage and such, even hanging upside down from it, is good excersize for them.
6. He will eventually come out on his own, he feels a little scared right now and wants the safety of the cage but with a little time he will come out, you can try giving him a treat to entice him though.
7. Grinding is normal, most all birds do this, usually before they go to sleep.
Sounds like you have a normal grey, but you need to work on his diet, only sunflower seeds is not healthy for him. Hope this helps and keep us informed on your progress. Get us a photo of him if you can, we love looking at other's greys and maybe it will answer the question of age.