Is there a way to determine the age of a black hole. Suppose 100 Billion years from now, if two black holes have exactly the same mass(say 30 M☉). One of them formed 10 Billion years from now and other formed 20 billion years from now. At t = t0 + 100 Billion years, looking back into the past, Can we predict how old these black holes are ? Is rate of dissipation of Hawking radiations any different for them?
From looking at the Black Hole alone, there is no possibility of determining its age. The state of the Black Hole is fully determined by a few fundamental variables (mass, angular momentum and electric charge). This is the statement of the famous dictum A black hole has no hair. Hawking radiation in special is only dependent on these variables.
You may be able to determine the age of a Black hole by indirect means (e.g., by looking at its surroundings and see how much it is cleaned from matter).
No you can't say anything about their ages and yes, their Hawking radiation is different... not that you could detect the difference. In more detail:
If your two black holes began with identical mass, but at different times, the younger hole would have lost less mass than the other through Hawking radiation, with an age difference of only 10 Billion years the mass difference would be unmeasurable (with current technology).
If at some point in the distant future two BHs of different masses are encountered, one could not in general tell whether they had been born at the same time with different masses, or at different times with the same mass.
The intensity of Hawking radiation depends on the temperature of the black hole and as a BH evaporates it effectively heats up, and as it heats up it emits more and more Hawking radiation leading to a final burst before whatever happens right at the end.
So it is also true that the older black hole, having lost more mass, will be at a slightly (but unmeasurablly so) higher temperature.
However, I have neglected the temperature of the cosmic microwave background, so far. That is currently about 2.7 Kelvin and until the expansion of the universe has lowered it to below that of a black hole, the black hole will actually absorb more energy from the CMB than it emits through Hawking radiation and will actually have increased (immeasurably) in mass.
This is why it will take of the order of 10^100 years for all black holes to evaporate, compared to which even your nominal 100 billion year interval is a drop in the (cosmic) ocean.