I've been lifting for a few years and biking but want to take up running. I ran for the first time in a long time and did a 7:35 mile yesterday and was breathing a bit hard for the whole time. Is it likely I can do 3 miles in 22-23 min if I train for 3 months straight? Also, one of my biggest problems yesterday was shin splints. They were tight as hell for a few minutes after the mile. Anything I can do about that, or does that go away with time?