Five years would defiantly not be a few years in skin terms, but if you think about pregnancy womens stomachs are only stretched out for a number of months some leave saggy skin and some don't it all depends on the elastic in the skin and thats something you can't worry about because you won't know just take things slowly and take maintenance breaks to allow your skin to slowly readjust. Don't do endless cardio, weight train, tone as much as possible.. make sure your diet is super nutritious not just low in calories or carbs and you can sleep at night knowing that you are doing the BEST you can, if there is a skin issue in the future you will cross that bridge when it comes
as for now you ARE young plenty of elasticity in that skin don't fret. There's a chance that I could have some skin issues but I can't do much about it, I don't beat myself up over it or even think about it, there's more chance that I could get knocked down by a car when I go outside but If I thought about it all the time I'd drive myself crazy.
Oh and my boobs have sagged as well and im only 21 from weight loss, they don't take to it well I believe, arms are like that also them and tummies (sometimes thighs) are just awkward areas!