I'm a "former young man" too. There is no age to be acting well or badly with regards to this debate, and there isn't even an absolute metric for how well or badly one does when it comes to the issue.
But I know I don't need to change to a new smartphone every year, likewise for my laptop.
I know the next time I get a smartphone (in years), I'll be much more likely to accept something of lesser polish for something which allows me to replace parts easily.
I know that my beef consumption is not an essential part of my life in the sense that I'd die without it, it's an accessory of pure hedonism, and I still don't entirely avoid eating a good steak every once in a while but I put mental efforts into curbing such consumption.
I keep in mind very strongly the strategy I want to adopt regarding the place I live in and the places I could work at, such that at equal levels of satisfaction I don't pigeon-hole myself into a place where a car would be an absolute necessity. Each person's strategy can change, but things to take into account include access to public transportation, remote work even partially, only partly using a car along the way if really necessary, and so on.
I'm keenly aware of the amount of plastic packaging around me and whenever I can I will prefer avoiding such products. Likewise for anything that can be refilled: do you really need to buy the same container for your detergent over and over again? Why not refill it if you can? etc.
I keep in mind all those issues when the time comes to vote, and in my own way strive to encourage this sort of awareness in the people supposed to represent me.
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The list is entirely dependent on each person, but you can only start to make that list and to think constructively if you acknowledge the problem and leave aside nihilism and apathy.
I don't want kids, but that doesn't prevent me from having the awareness that the things I do (or don't do) can and will hurt other people's kids. Using my age as an excuse to not give a crap is disingenuous. Using the observation that others aren't pulling their weight either is disingenuous. I can't force others to do something but I can change what I do.