Fixing age groups so the two populations have similar age structures

Is this possible? For example, cancer registry data have age groups cut off at 4s (i.e., 25-34, 35-44, etc.). If a sample population provides data with ages of 5 as the cutoff, how can I correct this so it has similar intervals to the cancer registry data age intervals? My overall goal is to indirectly standardize the study population for which I have total observations and age structure; however, if it doesn't match the same age intervals as the standard population, what's the solution? Thank you!
Perhaps you could try constructing cumulative frequency curves (piecewise linear or fitted curves?) for both and then reading off the quantities in each bin matching your chosen bin limits. Nothing is going to be exact.