Do not worry about dual citizenship, he has the US side as a right. If he has to "renounce" that for the Thai authorities, he can always re-apply for a US passport later if that is what he wants.

The problem is that Section 11.1 can only provide exemption from Section 10.4 (5 years' permanent residence) and Section 10.5 (singing the National and Royal Anthems). So even if he became a superhuman golfer or some such, he would still need to be at least 20 years old and have a profession in Thailand. I believe the minister has the authority to override ministerial regulations but not the Nationality Act. Therefore he might be able to relax the requirements of evidence of a profession (i.e. work permit, tax etc) for a sportsman or other superstar but can no way reduce the minimum age from 20.

One possible example is Ananda Everingham, the Australian-Lao actor, who is a star in Thailand, but he was already in his late 20s and presumably did have some kind of work permit arrangement in Thailand and probably had PR tagged along with his father from when it was relatively easy to obtain. I think Ananda could meet all the requirements in the regulations but I am sure his stardom enabled to get through the queue in record time.

An American brother and sister, who had grown up in Thailand as children of missionaries who lived with an aboriginal tribe in the jungle somewhere up North. Both petitioned the government to give them exemption from the requirement for PR under Section 11.1 and I think the girl needed exemption from the minimum age when she first applied. The distinguished service they wanted taken into account was the sterling work they had done with the aboriginal tribe in helping prepare a dictionary and grammar of their language, educating them and assisting in their efforts to obtain ID cards, employment, healthcare etc. Needless to say the government doesn't give a monkeys about aboriginal tribes or foreign missionaries who encourage them to cause trouble for local government officials. The brother and sister were totally fluent in spoken and written Thai but both petitions were dismissed out of hand. The story had a half happy ending because the sister, who was born in Thailand, eventually obtained Thai nationality after the 2008 Nationality Act which clarified conditions for aliens born in Thailand before 1992 to obtain nationality. Her brother remained out in the cold despite his continuing distinguished services but i think he might also be able to squeeze through under the 2008 Act due to a Thai wife.

I think Section 11.1 is essentially redundant because anyone in that category would no doubt have access to a fast track to PR and then citizenship anyway.