How things are determined or more like should be is by the Family Law Act.
Family Law Act, R.S.O. 1990, c. F.3
Please read and in particular the section Section31(1)&(2).
Most agreements have conditions such as his did but if you think about it all these are doing is stating ways of the same thing (pts 3,4) The most important to include is #1 as the primary condition for termination of support.
1. The child turns 18.
2. Completes a Max 4 yrs consectutive post-secondary
3. Becomes self supportive. (ie working.)
4. The child marries.
5. The child dies.
6. The child ceases to be a child of the marriage.
# 6 is basically redudunant and in my point of view should not be there. But I am not a judge. My spouse was held in a default hearing for the last 6 years mainly over this last point. The judge clarified and ruled on this point on Dec3/08 He stated that child of the marriage means that this child was born to the parties named. In his opinion it had no other responsibility. I think the only thing that could end a condition like that would be if the father were proven that he was not the biological father.
The family Law act also states that at 16 it can end but that would have to be say if the child moved out and is supporting self or if the child applied and was emancipated.(extremely rare happening these days)
My advice is to have the draft rewritten to include the first 5 points.
Also have this section make reference to the section of the act I mentioned earlier.