Today's Sunday Times has this article: "Over the Hill at 50?" While there is much talk on youth and the future generation (today's youths), the older generation may well feel left out, even for those who are just turning 50 or in their early 50s. Are you past your prime when you are 50? For Christians, the answer is definitely No! In fact, the 50s and 60s could be your prime. By then, you have known the Lord for 3 or 4 decades, even for those not born into a Christian family. Experience comes with time, especially time in the Lord. One of the requirements for an overseer is that he is not a novice (1 Tim 3). In 1 John, it is the "fathers" who have known the Lord from the beginning. One has to be tested with time and I doubt whether it is advisable to appoint anyone as elder or pastor if he has not been a Christian for 10 years.
If you are serving in a Seminary as lecturer or professor, it is unlikely you are in your early 30s unless you come to the Seminary straight from graduating. An ideal Seminary professor should be one who has known the Lord for a length of time, and he has done post-graduate study in theology (this takes time). Often for most lecturers, from an undergraduate degree to a doctorate in theology takes 15 to 20 years. This is due to time spent in ministry after a Bachelor degree and then some even stop at Masters and serve in churches again before going for their PhDs. By the time they gain their doctorates, they are likely to be in their early 40s. This means after some years in teaching, it is only by their 50s that they are established in their teaching ministry as professors of theology. Not to mention some of the professors come from a professional backgrounds in other secular work which no doubt is helpful in Seminary teaching since most church members are working people and it is important that professors know at first hand what goes on in the world with all the struggles and challenges.
Hence, it is only in the 50s, some find that they are in their prime. With people living longer nowadays, I can't see why those in ministry can't serve until they are in their late 60s or early 70s, health permitting. I know citing Moses as an example is not exactly a great model in the modern world, but Moses started when he was 80 years old and when he had completed his 40-year of service, his strength was the same as when he started, by the grace of God. He could have gone on for another 40 years if God had allowed him to enter the promised Land.