Hi Pinfada,
I work for the petroleum industry, so the experience of the workforce is critical to our operations. I've encountered the same situation as yours a few years back.
Based on the data, I came up with the projected number of people retiring and from which trades/skill group they're from. It was hard for us to accept that we would be losing people, i.e., more than 100 people within 10 years (assuming people stay until their retirement age). We just had to do something then.
Given the projected number of retirees, I gave two options to the management. Either we recruit people at the point of retirement (hence, no change in the number of the workforce but a great loss in terms of experience) or recruit people way ahead of the time we need them. In the second option, my lead time is 5 years ahead. The management finally agreed on the second option, and it became our long-term recruitment plan.
At any point in time, we have more people than we actually need (a buffer) to address future concerns. The disadvantage, of course, is that the company has to bear extra costs to maintain a higher number of staff, but it pays off in the long run as we minimize the loss of experience.
Hope that gives some insight to you.