Question
9 y ago I got seeds from procing lemon tree from a friend of mine.  He said in 5-6 years they woould produce. So far I got no flowers let alone lemons.  Plants (6 of them) look healthy, no bugs infestation, they stay indoors (Colorado). Comments pls.  Thanks  Anne

Answer
Seed  grown trees don't usually bear fruit.   If they do it might take up to 15 years (normally 7-15 years)for a tree to become mature enough to fruit. When a tree is grafted, the scion or fruiting wood is capable of flowering at a very young age since it comes form a mature tree. Grafted trees take about 3-7 years to start producing flowers. If you like the trees keep them and fertilize them which will speed up the flowering process.
Fruit trees need to be fertilized 4 times per year with a citrus and fruit tree fertilizer.  Feed it citrus/tropical fertilizer March thru Sept. Check with your local nursery for a citrus fertilizer.