on season 4 episode 9 when tony has surgery on his arm lorena tries to hit on that doctor guy but why would he go for her if he probaly way older and she a high school girl? plus i never got it how can they be in hs for 5 years if when it started they were already like 16 and 17

Because its TV. Other examples are Welcome Back Kotter and Head of the Class. Sometimes logistics does not play a role the situation is what makes for the show. The elements within the series and pulling more stories out of the elements and excluding logic sometimes may play a part to get what one needs.

Kelli Packard was only 16 when she enter this show and played 16-year-old Tiffany, the main actress playing the main character of this show, back then and she looked hot.