How long will i get better like this?

I have been playing tennis for about a year and 4 months now and i have improved very quickly. I am about a 4.5 as of now....how long will this wave last? i am 20 years old and i have placed in one challenger event.....how good could i get? My goal is to go pro in 2 years...i will be 22 then i know its late to get started but is it possible?