By Evan Bleier Although his own NFL future is undetermined, Rob Gronkowski shared his thoughts about how long his longtime teammate Tom Brady will keep playing pro football during an appearance on Jimmy Kimmel Live!. The 32-year-old Gronkowski, who played nine seasons with Brady in New England before joining him in Tampa Bay, said he initially thought the NFL’s oldest quarterback would sit out a year before ending his “retirement.” Instead, 44-year-old Brady returned after about 40 days (likely after confirming former Tampa coach Bruce Arians would be gone.) Now that Brady is back, Gronkowski …