He's middle-aged, so was likely in his 20s at the youngest when he defected, as he was in the woods for 15 years. And its not like he was even high chuunin when we met him, Hazou became better at Taijutsu than him before the chuunin exams.
It took him about 4 months to complete Summoning as well (though in fairness that's mostly our fault, we were busy and he lost some progress because of it.) 250/2xp = 120 days or 4 months
It will probably take him the better part of a year to even get SC to 30 so his XP can actually benefit from it, so it would take even longer to learn earth
Maybe if a talented Arachnid ninjutsu spec teaches him earth he can learn it faster...
It always costs 1k to learn any element. This has been said several times now. You get 500 back to put into jutsu, so on the sheet the stunts section will say 500 XP spent on the element, as the other 500 is put into skills. But you need 1000 XP every time
EDIT:
Here is a hypothetical Kagome build I did a while ago. I think it's a decent approximation but it is hard to say for sure
docs.google.com