Older dog acting strange.

I have had Dakota since he was 3 months old and he will be 12 in January. The last couple of months his behavior has done a 180. I have two dogs and I have always been able to leave food in the car and they would never touch it. The other day I was in a store for about 10 min. and in that time he ate a whole bag of hot dog buns and a small apple pie. They never bark when left in the car and know not to get in the front seat. Now he barks aggressively at anything OR sits in the front seat and just kind of yips. He has become very clingy and wants to be in my lap if I'm sitting down or follows my every move when I'm up. He eats well, plays like a pup (second puppyhood?) and is in good "physical" health. The other day he got out of my backyard and I was working in the front. He didn't come up to me and I didn't know he was out until I heard a horn honk and looked up and he was standing in the middle of the road just staring at the car honking it's horn. Wouldn't move until I called him. His hearing and eyesight are fine. Is this a form of senility that just comes with age or is there some supplement or vitamin that would help him.

Thanks.