We've talked this to death in the forums. Some provinces do have laws (age 12) and others have none.. but ultimately, you need to be a physically developed adult to ride in front of an airbag. When vehicle manufacturers design vehicle protection systems, most are designed to protect adult passengers. In many cases, from a 5th percentile adult female up to a large adult male. The 5th percentile Hybrid III dummy is 108lbs, 59.1", and has a seated height of 31". I suspect that if you look for data, you'll find that the 5th percentile adult female dummy doesn't do as well as the other adult dummies in crash tests, although primarily when seated in the driver's seating position due to their decreased distance from the dash necessitated by shorter legs and arms.
Since many 14 year olds are not yet physically developed adults (puberty has not yet completed), they should not yet be driving in front of a single-stage airbag..or potentially any airbag. So while I might be comfortable with a 14 year old in the front passenger seat, and I'm definitely comfortable with any post-pubecent adult in the passenger seat at 5'+ and sitting far back from the dash, I'm not so sure I'm comfortable with either driving in front of a single-stage airbag.
Can you imagine if you had to be 170lbs to sit in front of the airbag? Most of the Canadian population would not be able to drive... considering there's MORE danger in the driver's seat than in the passenger seat.
-N.