Is it possible to....

There is unfortunately no built-in setting for that, but these information are stored in the game definitions file. You could open the definitions.db with an SQL editor and modify the "plants" table (which contains the growth times for all plants).

What do you mean with "real-time growth"? You certainly don't want your trees to take 50 real time years until they're fully grown

The "growTime" column contains the amount of real time seconds until the particular plant reaches the next growth stage. For instance, the "birch_sapling" has a growth time of 11500 (a bit more than 3 real time hours), then it becomes a "birch_s0" (which is a small birch tree). The "birch_s0" plant has a growth time of 6500 (almost 2 hours) until it becomes the "birch1" (a fully grown tree). So in total it takes around 5 real time hours until a birch tree is fully grown