Yesterday when I was practicing I "felt" something when i was lunging forward against opponent's drop short. I"m not injured, nothing happened, but I am approaching 30 and I never "felt" something on my Achilles before in the past. I feel like If i do that few hundreds of time in the future, it would eventually snap my tendon. So any stretches and exercise to prevent that from happening?
I just wanted to highlight one phrase in scrubplayer's post. He is NOT INJURED.
No need for a doctor if not injured. It is hard to hurt that tendon to the extent you were describing. Strengthening the lower leg will make the calf muscles stronger. Walking, running, jumping, TT footwork, any footwork training drills, regular playing of TT, especially at the level you play at scrubplayer, will continue to keep strengthening that tendon. If it was mildly injured, you should know, soft tissue grows stronger fastest when some damage has occurred.
So the incident you described, which made you think and feel, but did not cause injury, that in itself would make the tendon grow stronger provided it has enough time to recover before the same action is done to the tendon. Tendons take longer for your body to repair than muscles.
By the way, what I said about soft tissue is true for bone as well. Just like soft tissue, bone grows stronger in direct relation to how it is stressed which is why, when someone in their 40s or 50s or older starts having OsteoPenia (precursor to OsteoPorosis) they are told to do Weight Bearing exercises. After a bone is broken is actually when it will grow fastest and strongest. The area where a broken bone grew back together is almost always stronger than the bone was before the break.
Our bodies grow stronger in direct response to how they are stressed. If you did that action once every three months, to only one of your Achilles tendons, that tendon would end up dramatically thicker and stronger over the course of two-three years than the other. Just like, if you play TT a lot and you hold up both arms and compare them, most likely your dominant hand arm (the arm you hold your racket in) will be larger than the other arm.
Don't worry about this. Just don't do it again for another 2-4 months. If you did it once or twice a week for 6-8 months, you would end up with a repetitive stress injury to your Achilles that would be almost as painful as if you had a tear (not severed but torn). [Severed would be a complete cut of a tendon in two separate pieces; a tear would be part of the tendon getting a cut but not all the way through; A tear is much much much more likely than you severing that tendon, unless a sharp object like a knife, {or an arrow LOL} was involved.]
Likely you are strong enough that what you did should not matter. Just keep playing and show us new footage of you beating higher and higher level players.