Nope, age will not force a spawn, some people own clownfish for many years and they never spawn for them. Tank conditions are the second factor, everything from feeding to temperature to light cycle can make a difference.
If you got your clowns that small they were most likely not even 6 months old yet (kinda sad to hear, most breeders wait that long to sell the babies) so they are most likely still under or around 1.5 years old. The time is getting close thought as females can spawn anywhere from around 1.5 years old to 2.5 years old. Males can fertilize as early as 6 months old (as reported by Doni).
Conditions in the tank will matter though, they need a suitable spot to spawn (sometimes its the glass, others a good flat rock or surface). Higher temps (82-84) will help induce spawning as well. Increased feeding will help push for spawns as well as make stronger spawns (if you intend to raise them), so a variety of food often is best if that is what you wish to do.
Another thing is a longer light cycle, increasing your light cycle up to 10-14 hours can help induce spawning as well. (has to be consistent though).
If you see your fish cleaning a spot on the rocks or glass pretty constant then they are usually close to getting ready to spawn. Hope that helps.