Exactly. The only excuse one has to be voting at that age.
1. Military service.
2. Age 30, plus one of the following:
2a. Land ownership. 2b. Business ownership.
2c. Income tax payer with taxable income in 7 consecutive years. (Assuming that we keep the income tax, of course.)
There could be a petition process so that citizens not meeting the criteria can seek the franchise, but the bar should be quite high. After all, few people who do not meet the criteria would be productive citizens.
Finally, the franchise should be denyed to or removed from anyone receiving public assistance (apart from veterans benefits) as such transfers of wealth create a conflict of interest.