To point at first my question has a part of trying to make a concept and is not about was there a Big Bang or not. We accept expansion so it is right to think about a starting point of expansion and I am not concerned about that. I doubt about time elapsed between the Big Bang and the present time! Please consider this before You read my question. My question is partially a try to answer. Now the question...
If we think about all the most distant objects from Earth we get a spherical area of radius 13.8 billion light years. Now if we have such a group of objects present like a composite object due to measurements it must be old like every single part of it, at least time for light to travel to Earth: 13 billion years. So from this sphere to 'now': 13.8 billion years.
Now we must add time between Big Bang and the '13.8 billion light years sphere'. If we presume speed of light from central point to area of that sphere that is 13.8 billion light years to add. But massive objects have not that speed so let presume a factor between 0.5 and 0.8.
There is the space inflation also to take in account so the factor rises. The whole inflating observable universe has a growth of speed slightly less than c and thanks to that the objects can be seen from Earth but very close to c because we see the red shift of these objects, so time does not change much from 13.8 billion light years.
Finally adding time between Big Bang and the '13.8 bly sphere' to the time from '13.8 bly sphere' to 'now' gives 13.8 by + 13.8 by = 27.6 by.
Is this concept right?