Definitely agree. I think in 18 months u could hit 2:50
Build your mileage up I would say sub 3 is attainable but you wil have to put in the time and make sure you stay on top of your health so you don't get injured like in the past. Start slow & build your mileage up I would say start with 20 MPW and build up to 60-70 over the next 6 months. After that start focusing on getting in good workouts. 1:18 is good for a soph
In Hs & your lungs should be recovered from smoking within a year of quitting smoking ( I wouldn't worry about it because what's done is already done)
Once you get your mileage up lose some weight & get some good work in I'd say you could be in 2:50 shape in a year or 2.