I think it depends on what exactly you mean by athleticism. What are you looking to accomplish, exactly? Are you looking to be able to distance run at the same speed/ intensity as before? Do you want to regain all your pre-surgery flexibility? Do you want to be able to play sports at the same level as before? If you specify exactly what you want to know, I might be able to answer the question in more detail.
I did 8 cm lengthening in my femurs with Stryde nail back in 2019. I can tell you that, within the 1st year into recovery (so by the end of 2020), I was able to fully run/ sprint. I was not as fast of a runner as I had been pre-surgery, but I also did not actively train/ work hard to regain this pre-surgery speed. Frankly, I didn't care that I couldn't run quite as quickly (the height gain was much more valuable for me).
However, I could and did engage in athletic activities (running, basketball, etc) and participate in them to about the same extent as I had previously. And I found that if I trained hard at it, my gains improved.
So long story short, I think it would be difficult (perhaps impossible) to become a professional athlete after a surgery like this. But you could regain your prior levels of physical conditioning with time, energy, and determination. I'm thinking 2 years post-surgery, you could be very close to your athleticism prior to surgery, even if you lengthen a lot (like I did). It is not easy, but an achievable goal.
And remember, removing the nails from your femurs (which you should do roughly 1 year after surgery) also facilitates your athletic recovery. Hope this helps. Please let me know if I can clarify anything for you and I will do my best to do so.