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I saw that duelbits send reward from time to time to gamblers who are active on the platform. All you need is to check notification centre more frequently. Know that rewards have expiration time. But never heard that bonus have wagering requirement. However, this looks fair, but to get 5 bucks gambler must wager 5k - this looks unfair

I don't think that it is unfair. It is free, afterall. I just hope that they make it lower. A jumped from $1000 to $5000 is so hiighh. Maybe around $3000, or maybe $2500. Anyways, it's on descrition. And it's free, so shouldn't complain.
This is their promo codes from Telegeram, you can check them out.
Absolutely...it is quite normal to have wagering requirement in order to claim bonus drop. $5 with $5k wagering requirement is still considered as reasonable because there can be higher wagering requirement in other casinos for the same bonus drop. It looks increased much from 1k to 5k but I believe there is a reason for this adjustment. Nothing is completely free, bonus drop is a bonus for our gambling activity only and we should not force ourselves to wager just to be eligible for it.
It is still low compared to other casino that requires $7k to $10k wagering just to claim their bonus code of $5 but I don't blame anyone for thinking that it is high since the last time a person can claim only needs $1k wagering. A 5x increase in wagering requirement is pretty high though, it is a requirement that needs a 500% increase in wagering activity which can catch any gambler to a surprise.
33 is a peak for a regular men. Professional athletes have their peak lower (for example at artistic gymnastics athletes professional athletes retire at 17-19y.o), because they always put their body on the limit, their body exhaust more. If they were machines, then they have huge mileage. Like taxi cars breaks or die faster than regular cars

Why football players retire early - probably due to muscles structure, flexibility, body recovery phases and etc.
It is the competition that makes football players retire early. Since football is a battle of wits, skills, speed and endurance. Younger players have way more advantages than the aged one in terms of speed and strength. So older players who had lost their speed and endurance to compete against younger players may likely retire and be offered as training partners or coaches of the younger ones.