I get the idea of Steve Rogers going back in time to be with Peggy, but I thought the Super Soldier Serum stopped him ageing so how come he was old when Sam and Bucky saw him again?

And another thing before I forget. Why did Cap give the shield to Falcon and not Bucky? Sam Wilson was already a core Avengers member and great superhero, but Steve and Bucky had been lifelong best friends and Bucky is was best known at the time as a face of Hydra. In my opinion it should have been Bucky.