A couple thoughts about age and effectiveness...
I once heard someone say that we don't really settle into our personalities and who we are as a person until we reach the age of about 30. Really? That is amazing because we make so many life decisions before we reach 30 (well, many of us do): Our majors. Our mates. Our career path. Our decision to follow Jesus. Perhaps this is why so many of us change majors, change mates, change careers, and change in our commitment to Christ. Perhaps.
I also once heard someone say that they felt their most effective ministry years would come when they reach their 40's and 50's. Wow! This same person mentioned that Moses was called back to Egypt at the age of about 80.
Young people might often think of their ministry "prime" coinciding with their physical "prime"--in their mid-twenties. But that is probably NOT going to be the case. At least, we should hope it isn't! Hopefully, we'll all be serving God for many decades after our 20's, and it would be sad to think that our effectiveness would be going downhill the whole time. Unfortunately, we tend to place too much value on two things: 1) The "ability to relate" that young people supposedly have. 2) That the youth in a society are the prime targets for ministry. Perhaps I'll write more on this at another time.
I look at my own ministry here in 5-year chunks. I feel that my first five years on the field (in a different culture) were to learn the language, learn the culture, and begin to form ideas about the ways to increase God's kingdom and make a real impact on this society (rather than just doing a ministry). My second five year period was the process of getting things set up, putting pieces into place and getting ready to really make a Kingdom impact (still, doing ministry concurrently). The third five-year period has been the fruit-bearing period--the time when so many things come to fruition and the impact that I dreamed about before I ever came starts to become a reality.
Now, this teaches us a couple things. First, I think it shows that we cannot imagine or expect young missionary recruits, with no field experience and no fluency in the language, to have their strategy all mapped out before leaving for the field, or before spending enough time to become fluent in the language. Secondly, it shows us that to make a lasting difference we need a long-term approach.
Perhaps a fourth five-year chunk would be the time in which I have successfully worked myself out of a job--when the nationals have been trained and inspired to do everything that I might do myself, thus rendering me unnecessary. This is what we call a success in missions.