Indian Star breeding age?

[Torterra]

My older female star showing breeding behaviour, she is mounting the little 2 year old and generally ramming her around ( the little Margo is only 290g).
They spent all winter peacefully sharing the same table and the same light, no trouble for months.
Here are the big female and the little one basking together during peaceful winter months

I am thinking of separating them, but the little one is not seems to be bothered at all, she gets her share of food and heat, and gaining weight normally. If I was to separate I am thinking maybe I can put 3yr 4 month old Mitha with the Mango, my male. Male is only 2 years 3 month old, he is 380g and Mitha (female) is around 1350g. Must I give them few more years to grow more or will it be good for them to start a 'family'?