How old should I be when I get my first formal job?

A lot depends on the job! I started mowing lawns for a set group of customers when I was 14. I had friends that put themselves through college by expanding their lawn mowing service into a big operation. At 16 I was a stock clerk in a department store. At 17 I was a construction worker. At 18 I was a warehouseman in a huge plumbing supply operation. After that was college and 22 years in the USAF doing all sorts of jobs with increasing responsibility.
If you can show up on time, do good work with a good attitude, and present yourself well -- then there is a job somewhere needing you. Obviously there are age related requirements that limit some jobs, but as you get experience, (and a good reputation as a worker), more jobs will become available.
I run my own company now. The basic skill set is still the same - show up on time, do good work with a good attitude, and my shop looks professional.

In my opinion, the younger the better. My children started their newspaper route at the age of 9-10. This of course is part-time and still allows for school work and a social life. But the habit of working reinforces many great qualities/characteristics (responsibility, financial management, respect, etc...) and should not be overlooked.

While there is no STANDARD age for everyone to start their first job, its important that you are mature enough to handle the responsibility of employment. Many young people are driven by financial need or desire for independence. You have to be able to balance your course work, athletic commitments, family and chuch/community activities so whenever you decide to get a job make sure you are prepared for the commitment.

If you're thinking about a job, you are probably ready to get one. Many industries have regulatory requirements (minimum age for employees especially) which they have to adhere to, but some may not. The experiences you get, especially starting out, may prove to be quite important later in life. I worked as a waiter, cook, commissary worker, and many other jobs when I was in high school. I think my first job was delivering newspapers (not much of that today) when I was eleven or twelve. The skills and interactions you learn (Customer service skills, responsibilities, work ethics, profit/lose) all travel with you throughout your life. Years later I would be Vice President of Customer Services in a very large transportation industry......
I was still using the same skills......with more experience, education and mastery.....still, the same skills.

As far as not knowing what you want to do, first jobs also will start telling you what you like and what you don't like to do.....Very few of us have the very good fortune to know exactly what they wanted to do. Good Luck!

I would say that work experience is valuable as early as you can qualify for the job. I have always been an entrepreneur...as young as 8 with my lemonade stand and creating craftsy things to sell. I also baby sat as often as I could. My first paid job was as a clerk in a small store. I had to be 16 then to take the job. I worked when I was in college as a replacement for the receptionist in a law office. As soon as I left college, I became a teacher and then a school counselor. I worked my way up in the district as an administrator and director of the guidance program. Now I am retired and still work in a small business as well as do counseling. I guess I would say the same as the others. Your skill set of integrity, being a hard worker, honest, on time and well groomed and spoken is invaluable anywhere. Being on a waitstaff is also excellent experience. You need to learn to handle customers well and manage complaints as well as compliments gracefully. Best of luck!
Marilyn Lowry