I would say about 30 years or so. So many risks and so many challenges that have never been done before, being that human lives will be involved. Just the thought of flying through space for 8 months and having to fight radiation, hunger, possible physical pains of just being up there, and always a chance of hitting space debris especially for a long trip. That’s just the trip, the landing alone would also present risks. Finally, there has to be a realization that those humans will know that there may not be a way back. The emotional distress that could set in could affect them drastically and reduce their ability to live and fulfill their mission. This is much more harder than landing on the moon. Hopefully I will be alive to see it happen but I will not get my hopes up too high (I’m 25 btw) but hopefully they are looking into it as we speak.