Having clowns does not mean you have to rush and find a nem. They'll live in soft corals, snuggle up to temperature probes, etc.......
..........Accepting all that, and being ready, [there is no magical number of months of tank age---it's far more the experience/skill/patience of the hobbyist] go, enjoy, and may it live long and prosper. But be ready!
I heard if you wear a sparkly ring the clowns will go for that in stead of your tender flesh. You don't want to do it for a once in a while attacker, as it can encourage them. But with an unrepentant assassin might be worth a shot.