Como é que se diz isto em Inglês (EUA)? The doors of the Tokyo 2020 Olympic Games volunteer activities are about to close. I understand the current situation. I’m disappointed tho. But I think I still have a slight hope for Paralympic Games. If I can join, I will do my best for someone.

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The doors of the Tokyo 2020 Olympic Games volunteer activities are about to close. I understand the current situation. I’m disappointed tho*. But I think I still have a slight hope for [the] Paralympic Games. If I can join, I will do my best [to be of help to] someone.

* "tho" is okay in text message, so I will it for now. The actual word is spelled "though" for formal writing. 😊

Even if I can’t join, the days I have spent and [the training experience have been invaluable*]. I appreciate >< the opportunity they provided. I have to move on. There will be another opportunity in my lifetime. (Before I die).
* "invaluable: beyond valuable.

I can’t wait [for] the next adventure. I’m not [going to miss out on] the opportunity. I will keep trying to grab something, [even though] I’m not young at all.

* "gonna" is extremely informal and used mainly by kids.