Every year, an RDSP holder gets an update about how much money can be put into their RDSP. The Statement of Grant Entitlement, says how much money and how much the government will match, with a Grant.

As you can see this is an important piece of information. I now know, in 2021, I can deposit $1000 in my son’s RDSP and it will be matched with $1000 in grants.
This amount will increase once my son is over the age of 17, as the income they will use to determine the grant will be his income, instead of our household income. When he turns 18, his grants should be much higher, due to his estimated income at that age.
When he turns 18, my son will also have to re-qualify for his Disability Tax Credit as well. This is what we learned from the last time he had to re-qualify. Luckily the rules if he should not get a DTC right away, have changed.
The Grant and Bond entitlement calculations will be based on your son’s income the year he turns 19 (not 17). However, for the year he turns 19, they will look at his income from the year he turned 17. They always use the income from the 2nd year previous to the year in question. So, make sure you file his taxes for the year he turns 17 and every year thereafter. Without it, the gov will assume his income exceeds the grant threshold where the entitlement is $1,000.
You will also need to submit a new government grant/bond application, preferably the year he turns 18.