WTF?... At my leanest in High School, I was wrestling 140's at 5'8", but I've always been the TST guy. My normal weight back then was 155-160. I haven't seen 160 in 20+ years. You must be thin as a rail. I did a bodyfat analysis recently and my lean body mass is around 160. I bet just a little light weight training would do wonders for you. Nothing crazy at first.
I heard something recently that's seems to be true, guys who can put on muscle easily, also put on fat easily if they aren't careful. My weight can shoot up in a hurry if I'm neglecting my diet. After leaving wrestling behind, I put on weight even though I was still active. I definitely was rocking the Kirby Puckett physique for a looooonggg time. People were always surprised that chubby dude like me could be so athletic. I know they meant it as a compliment, but it still stung a little.
I've always went to the gym, but I got serious last summer about diet and started running 5 days a week and it's help a lot. I'm tracking calories (In/Out) and it's working very well. The most important part for me about tracking calories is learning WTF is actually in the foods we eat. It's shocking at times to realize how many calories some foods have. Especially the kind of foods that are easy to binge eat.
I've pretty determined all the multitude of diets are pretty much bunk. If you're eating less calories than you expend each day, then you'll lose weight and vice-versa. I think the reason some diets work, like Paleo, Keto or Vegetarian, is because you're limiting yourself to foods that will fill you up quickly without consuming a ton of calories. I can eat a giant salad with a little chicken added and it'll be less calories than a Subway sandwich. And you're still starving after the sandwich, so you end up eating chips and maybe a cookie. So you're looking at 500-600 calories for the salad vs 1,200+ for the sandwich and chips. It's really as simple as that. The point is, when you start tracking calories, at least you know what's going on. So if you want to splurge on a meal and eat an entire pizza, then you can compensate before/after and earn it. Maybe up the exercise that day and the day after.
I'm currently at 190 and high teens (17%-19%) bodyfat. At 45, I'm feeling better than I have in a long time. Would love to cut down to 180-175 eventually, but I'm in no hurry. As long as I'm slowly losing. No need to dump a bunch of weight, then rebound and end up higher than previously.