This is the reply I got from AINP.
Dear sherry,
The Candidate and their spouse/common-law partner must both be between 21 and 45 at the time of application.
As a candidate, you may or may not choose to include your spouse/common-law partner as an accompanying dependent on your application for permanent residence. However, both you and your spouse/common-law partner must meet the age criteria (and language criteria) of the AINP under the Family Stream regardless of whether or not the spouse/common-law partner is accompanying the candidate to Canada. If you have a spouse/common-law partner, he/she will be assessed with the application and he/she must meet any required criteria.
If you have any additional questions, please feel free to contact a representative at the following number.
Alberta Immigrant Nominee Program
780-427-6419 (Edmonton)
1-877-427-6419 Alberta toll-free number
Hours of service:
Monday to Friday 9:00 am - 4:30 pm
She will be 21 in 3 months so you can apply after she becomes 21. no big deal about this. just matter for 3 months.