In any career path, there are trade offs. If you could work full time, every day, the guiding wages would not be terrible if broken down to an average hourly rate. You will not be building wealth, but you can get by. But the schedule rarely works out such that you are actually working full time (40 hours/week), especially when you're first getting started. A lot of guides have side jobs in the interseasons. There will be days that are long and hard and even if offered thousands of dollars for the day's work you wouldn't do it over again. There will also be days that you are having a great time with amazing people in amazing places and you'll be psyched to realize you're getting paid to have fun. Most days will be somewhere in between.
One of the bigger challenges is the effect it can have on your personal life. Maintaining a relationship can be tough because you will spend a lot of time away from home and away from phones/email - it helps to have a very understanding significant other. Though not all, many of my career guide friends are single. You also have little control over your schedule, especially when starting out - i.e. when the work comes, you should probably take it. Friendships can go the same way - you will be on the go all the time. You will form many great friendships among fellow guides, but you won't see them all the time. Be comfortable being on your own/doing things for yourself.
One of the best things about guiding, especially for the average early-mid 20s recent college grad (which is when a lot of guides start...and end their guiding years) is the time you spend with the clients. Most of them are older and wiser than you. In my experience, many of the clients are intelligent people that are successful and driven in whatever it is they do in life, and you can learn a lot from them. Pick their brains, ask questions, figure out what sort of career/life you might want if/when you decide to move on from guiding. And try not to let them pull you off of the mountain - some of them will try.
If you're young, try to get on and do it for a few years. Then you'll know enough about it to decide whether or not its something you think you can pull off long term. If its not, you will have learned some great people management skills that will help you in your next career. And some rope tricks, too.