So if we suppose that the cat country have the same laws as current real life Japan about drinking age then that means Rin is 20 years old as a minimum, meanwhile Nene is 12 years old, so basically Rin is like Mya-nee from Wataten, an university age woman falling in love with a girl roughly half her age. But well, the laws may be different after all, seeing how the 10 years old girls (the cat twins) are working full time like Nene and they started working there before Nene.
Also, we have got a characters sheet for this chapter, where it says the characters heights, with Rin being 170 cm tall and Nene being 101 cm tall, but truth be told even on that characters sheet Nene looks like less than half Rin height, so Nene height is more like "your height may very by scene".