If someone is 12 years old with size 8 us feet and is 5 foot 2 inches tall, how tall would you expect them to be?

Depends...: ... on lots of different factors, like parents' heights, your growth curve to-date and height velocity, pubertal stage, etc. That said, that height is above average for a 12-year-0-month-old male (months matter here). So all other things being equal (again, it depends on a lot of other things), I'd expect final height to also be above average for adult males, or somewhere north of 5'10" to 6'1".