Technically - You’re right: Solar Cycle 25 is due after solar cycle 24 finisghes, and hte “average” sunspot cycle” is 11-13 years. So, by math, solar cycle 25 might come that early “The really crazy part is that Solar Cycle 25 (not due for 11-13 years) is expected to be extremely weak by NASA..”
But solar cycle 24 hasn’t started yet (now, as of Oct 2008 we are still at the minimum zero sunspot activity between cycle 23 and 24), and nobody can predict when cycle 24 will even begin, much less end. Nor how high the peak of cycle 24 will be: It too may be as low as cycle 25 may be.
So, could we face 20-30 years more of cooling? Absolutely.
And I would bet on the side of 28-36 years of cooling - before temperatures even get BACK to where they are now. All previous cooling cycles this century have had 26-30 years of cooling, 5-10 years of flat, and 26-30 years of increase again, 5-10 years of flat, .....
When (notice I did not say "if") that happens, there will no longer be any particular talk about a cooling trend. The only problem I see now is that as the next solar cycle revs up and the sunspot numbers increase -- as they will very likely do over the next 5-6 years -- and then there is a new global temperature record in that period, climate change skeptics will blame it on the Sun. Timing is everything.