What is the lifetime use of a lipo? How many cycles/months/years until you retire a lipo and get some fresh ones?

My 2s in my rx8/pro4 combo seems to have very short run times maybe only 5-6 min. Had mine maybe 9 months, cycled maybe 4-6 times per week except for a 2 month period where i was busy crawling.

That was no specified period.
Never over-charge and discharge; storage it in a LiPo guard bag, temp is around 13 temperature, dry and cool place in 40% capacity; keep from acuity items, water, fire, etc. When you storage a long time, charge it to 40% per 2-3 months. Then it can be used around 2-3 years.

Of course, some accident maybe let it have a very short lifespan.

The lifespan depend on your using habit.

There's definitely a lifetime on lipo's. Sometimes manufacturers specify cycles.. It all depends on how important speed and capacity are to you. One rule of thumb is that if it no longer holds 80% of it's rated capacity you can consider it EOL. Generally you could expect around the 200-300 cycle range. Worse case scenario you put about 160 cycles in already. And that doesn't account for properly storing, etc... so you're probably about there.

5-6 minutes would definitely not be good enough for me so i would be replacing it with something bigger or newer.

What size (mah) packs are you running? In a heavy 4wd sct with high kv motor that might be about right on a large, high speed track.