I went cruising the world at 30. I am now 40 and I am still cruising the world.
I couldn't have made a better choice except that even in my case I am convinced that I could have started at 20! What I think is that when you plan a cruise of three or four years, be aware of the fact that for many of us, going back home and restart a normal life is really not desirable. If you travel the world with curiosity and interest towards other countries and their people and not only traveling from a marina to another marina together with folks of your own country, you will find unbearable the way of living and the way of thinking of those who never traveled outside of their country. Those who think they know the world because they watch tv.
Go now and meet the people of other countries. If you are smart you can live on 300-400 usd a month and will manage to earn that on your new life, mostly working on the boats of retired people...