Government provided open id service which guarantees age. Website gets trusted authority signed token witch contains just the age. We can do this safely. We have the technology. They could even do it only once on registration.
Digital id’s exist already in the EU, and many countries run a sign on service already. We aren’t far from this.
10k will not do much good on the grand scale of things. Once you start involving other people directly, the costs start skyrocketing. Be it if you want to bribe politicians, fund a revolution, invest into sustainable tech or just creating a bottle cap recycling programme, 10k just isnt gonna get you far enough. So focus on your own climate impact. I think the absolute best you could do for the most positive net good is to take inventory of your own carbon emissions and replace or upgrade whatever you need to lower them. Lower your heating usage by getting a heat pump instead of burning coal for example. This will depend on how low your carbon output currently is though.