When you decide you want a certain tattoo; wait 3 years. When you still want that certain tattoo then, go ahead and do it.
That's how I feel about it. I've been thinking about getting one for many years now, but still not taking it. Not because I'm unsure about it (I know exactly what I want and why I want it), I just don't feel the time is ripe yet. I'll have it for the rest of my life, what's the harm in waiting a bit