I think there's no harm in entering him at 8 weeks old, provided he's settled in well and is tame. There is the young stock class for a reason
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Honesty, breeder hams tend to do better in the main class than the pet class as the only pet hams that are entered in the pet class are ridiculously tame whereas Quigley might not (I'm not too sure). Jasper has done much better in his main shows than the pet show at Bracknell. You can always wait for Bracknell and Peterborough as well. I went to both last year and both were good fun.
Also, I just want to add, Quigley is a stunning hamster
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