Help me gain weight and also be fit

[slim]

I'm a skinny guy (it's in my genes)....I am 6ft and only weigh 160lbs. I want to put on about 20lbs but at the same time I want to have good cardio bc I'm getting a little older. So I'm about to join the YMCA and start working out. In the past when I was in my 20's I would work out but no cardio but now cardio is as important to me as gaining weight.

My question is this....does it make a difference in my goals if I lift weights and then go jogging on a treadmill right after? Or is it better to do weights one day and weights on another day. Any suggestions is appreciated. Keep in mind, I am not looking to be big and ripped....I just don't want to be so skinny.