You can age wines too long, but it depends on the wines.
General rule of thumb for white is 3-5 years is optimal, for Reds 6-10 years with some notable exceptions being considered long term investments.
For country wines, it's best to treat them all as white wines until you get a good idea of what's optimal. Your wines wont be the same as another person's even if you follow the same recipe, so you need to get comfortable with learning how to age YOUR wines. Do this by only drinking some of your wine each year. If it's not so good yet, then leave it alone for another year. If it starts getting good, then perhaps drink some more of it. If you practice good cellar management techniques you will drink your last bottle of wine just as it starts to decline in delicuousness.
Now bulk aging and bottle aging are considerably different, however you can combine the bulk aging and bottle aging to figure out the shortest time you want to age. Bottle aging is a bit faster than bulk aging you see, but bulk aging produces great consistency in the aging (meaning you wont have 25 bottles all taste different from one another), however it's slower.
I think bulk aging a long time carries a greater risk of infection due to how carboys are sealed, but it usually benefits a wine to bulk age 3 months to 1 year. So just care for the carboy carefully. Make sure you use a sanitation wipe to keep the top of it clean, and make sure the bung is secure and you should be ok. If the wine is over 12.3% alcohol, chances are it will successfully preserve itself anyway.