I think that depends on what opportunity is at hand. If timing is simply best due to a number of variables to enter after graduation, then great! For me, I waited 14 years. After about ten years in the workforce I found getting an MBA to be very rewarding and I could relate to every course of study. I also did very well academically and even coaches some of. Y classmates on projects and discussions. I would recommend 5-10 years. Some wait even longer and that is ok too.
I did graduate courses while working full time and was grateful for the work experience because I was not positive what graduate work I wanted to pursue. At the same time, I agree with Dra. Marisols statement , if you know exactly what path you want and have the financial ability , it might be helpful to jump right in after your undergrad work and complete your graduate work full-time -- without the stress of both work and school.
Good luck with your decision.
If you have clear what graduate program you want to do; for example, something you always wanted to become , there is no need to wait . However, I ( personally) recommend to work and practice in the field before pursuing a graduate degree. That will give you work experience and time to think about what your next professional goals are . Then, you will decide what is the best for you because we always change ,and sometimes people get into a graduate program and they don't like it afterwards.
I'd agree with the above, and say that there is no particular age that is "good" or "bad" to start graduate school. I started right after my undergrad program ended, although I also worked full time while completing this program. I'd say I loved having the learning in the classroom, with the application in the workplace for two years, especially while I was in the right mindset to go through school and remembered the effort it took to be successful on a graduate level.
Know whatever age you decide to pick up grad school, that it does require the right amount of time and effort. Life is always happening around us so ensure that you are prepared to go into a program and kill it.
Hope this helps!