Technically, it could get as big as 5' but that is a function of your weather, the length of your growing zone, availability of the nutrients, etc. That estimate is usually at 10 years though. So if you planted two twin plants, one in Chicago and another here in Texas, you would expect the one down here to get bigger faster at 10 years because our growing zone is longer. I have not seen LLs that are 4 years old but a 2 yrs old looked to be slightly more than 2'. The flowers were the usual limey color; you should limit the amount of light that it gets in order to keep them green longer (say 2 hrs or so?). If it gets a lot of sun then the immature blooms will turn white faster. Try pruning it every other year so pruning does not become an annual chore.