Thylacine

Hey everyone! Im a first time poster with lots of specific questions! Sorry if this is a bit long but Im really struggling. Im a 29 year old welshman who wants to move to Australia to be with his father,stepmother and sister.They have citizenship and my Dad owns his own company (he's a floor layer). They want me to live with them and my Dad wants to train me up as a fitter and maybe one day hand me the business.They will house me and keep me looked after tim I can get on my feet. As I have no skills that are needed,I was told the best option is a 12 month WHV and that I can apply to extend it before it finishes. All well and good,but today I hit a snag... I rang a visa agent to get the WHV and they asked if I had any criminal convictions. I was truthful and told them I had a ABH charge back in 2003 that ended with a 3 month referral order to a Youth Offending Team,a Common Assault Charge in 2006 that had 12 months probation and then two cautions for ABH in 2003 and 2005.All over 10 years ago Upon disclosing this,the agent told me I would not be able to get the visa. This has destroyed my dream to get away as I am no longer the same person I was over 10 years ago and just want to better myself. I have been to Australia 4 times since and its never an issue,they just have a 2 minute chat with me at the airport and then I go. Any help would be greatly appreciated as this is causing all sorts of upset!