Actually, any PHD worth completing is funded. Meaning you don’t have to pay for it 
People may be younger or older when they start their PHD. Some American students go straight from Bachelor’s to PHD but almost no international does since OPT allows them to gain critical skills that they may not be able to get in their country and since without OPT there’s no job for them in the US, it’s either get these skills now through OPT … or never.
However you DO have to pay for a Terminal Master’s and unlike U Edinburgh’s, which is relatively cheap, some can be quite expensive in the US since the main goal is to improve career prospects. 