You're assuming his education was publically funded - it might not have been. Can you say that he required the infrastructure or security to be successful?
So you're saying that immigration/emigration should be illegal? I believe people should be able to move if they want to if they follow the process. It's important that people can live under a government that they support and believe to be the best one for them.
It sounds like he has been paying his taxes all these years. So he has been contributing his fair share. Don't forget, him leaving means one fewer person for the government to provide services for. Knowing that healthcare costs increase as one gets older, this could be a large amount if healthcare is something his taxes cover.
Honestly, the logic that he owes society money for the past services is pretty convoluted. The government isn't keeping a tab of what people owe if they ever make more money. When then, would someone have paid their dues to society to earn the freedom to move? The people currently making money are paying current taxes. Are the kids in school paying taxes? No, it's the property owners, some of whom might not even have kids.
Tax schemes are designed to collect the amount that society needs as an aggregate. They try to be logical or socially acceptable in how they are collected. Society has not implemented a tax scheme saying you owe more for previous services because your income went up. They could, but they haven't.
