is it possible to avoid loose skin?

Did you get stretchmarks from gaining 100 lbs in a relatively short period of time? That might be an indicator of how elastic your skin is.

If I were you I'd lose the weight slowly, but also not put off starting the process. Your skin has it's best chance of bouncing back right now. The longer you wait, the older you get - and skin gets less forgiving with age.

I'm doomed I think, I get stretch marks very easily. I'm losing slowly, but I'm worried mostly about my lower stomach and my arms... UGH

Did you get stretchmarks from gaining 100 lbs in a relatively short period of time? That might be an indicator of how elastic your skin is.

I do have some very light stretch marks on my stomach but no where else. They really don't even bother me. so is that bad or good?

I would say that's good! You skin stretched to accommodate 100 lbs without without cracking so you probably have pretty good elasticity. I still have stretch marks just from just from getting hips and boobs when I hit puberty, so my skin...probably not so much. lol

wondering it there any older members who have lost 50+ pounds found what helps our ol'folk's skin?

I'm 60 and lost 58 pounds a couple of years ago, mostly from my torso. I sagged initially as though the skin all over my torso was a size or three too large, but have tightened up almost completely since then. No obvious evidence of loose skin shows up in the mirror at all now, so long as I keep my still somewhat misshapened belly button covered with the palm of my hand. Well... my boobs sag, but I am 60. I probably could have expected that in any case.

My big worry wasn't loose skin, which I didn't even think about until more than half of the weight was gone. It was muscle loss. I had been naturally slender as a young adult and blamed metabolic rate lowering muscle loss from advancing age and the change in my hormonal status for the fact that I needed to lose weight in the first place. And I knew it would be really hard to regain any muscle at my age, so I was strongly motivated to hang on to as much of my remaining muscle as I could. That meant:

A well balanced, nutrient rich diet with plenty of protein.
A moderate calorie deficit, aiming for a pound/week loss for the first 30 pounds or so, then a half pound/week.
Strength training, typically around an hour per session, 3 times a week. I used the resistance machines at the gym.
Rarely more than a half hour at a time of steady state cardio, which can shred more than fat if you over do it.
I ate back my exercise calories (At least 2/3rds to correct for MFP's obviously inflated estimates).

I think all of that benefited my skin even though that wasn't the primary motivation. The one thing I did just for my skin was apply coconut oil from head to toe after every shower, which - if nothing else - is at least a great moisturizer.