Lime from seedling to be grafted onto lemon tree

[Popper]

So i have this lemon tree whose fruits have quite a thick skin and are not the best of qualities... Managed to get some indian lime tree seeds and planted those to have these 2 beauties growing and wantinf to eventually graft the lime onto the lemon main trunk... How old should the lime trees be to be used as scion wood?

 

[cpp gardener]

They're probably big enough now for bud grafting. For cleft grafting wait another year until the stems are about 1/4" thick.