I would definitely say that the prime friend-making years are at school and college. After that it slows down dramatically.
For those that were born into the truth and left the organization, it is infinitely harder to find and keep friends. The loss of all JW social contacts leaves just the workplace as a starting point, and if you happen to work for yourself you don't even have that.
That's why I value this forum because having left the JWs I have met a couple of people on here who I have met in person - we all share a common experience.
It takes courage and a willingness to seek out new friends, wherever they may be.