I started doing cardio about a week ago, Im pretty out of shape 5'11 210....Anyhow im not trying to outdo myself so I walk at around 4mph,,,This gets my heartrate up to like 145-150!! Anyhow yesterday I noticed this older fella walking the same type of setup as me 4mph no incline and he had been walking for about 20 min more than me but his heartrate was only 112, should this be something i should be concerned about?? I had a full heart checkup lastyear and it all came up fine some im wondering what the deal is, is it where Im just so out of shape?

You're out of shape and your body is not functioning efficiently when exercising (or in general for that matter). Don't be too concerned with your heart rate. remember that everyones body is different and responds differently to similar exercises.

Just keep walking on the tread mill. As long as your heart rate isn't skyrocketing there's no need to worry. Your body will become more efficient as you continue to workout. Remember not to get stuck on the treadmill only! Weight lifting and diet are gonna be important with your weight loss as well. Switch up from walking, to biking to erging if you can