Will there be a race for my age group at a National Classic or regional race?

It isn't guaranteed. Under sections 17.4 and 18.4 of the Cycling SA Road Cycling Handbook 2026, at National Classics (Category A) and Regional Mass Participation events (Categories B to D):

• U17: a separate U17 race category should exist wherever possible.
• Younger youth categories: youth race categories are encouraged, within the youth distance limits.
• A youth race may be held on the main route within the allowed distance, or as a separate criterium.
• Categories can be combined, subject to the distance restrictions.
• The President Commissaire may allow support vehicles for U17 and youth races, depending on the course, number of riders and rider safety.

Day membership: a rider on a day membership can't race in the specified age categories or win prize money at A, B or C category events (section 9.7.4), so you need a Cycling SA membership to race your age category there.