Well, I can answer your title question: at what age did we start? But I can't say if those are the right ages for your kids.
My son (firstborn) was started around age 2. Maybe slightly before. No previous potty training experience for me, and this was in the burgeoning age of internet, so we didn't have it and I had no online resources to look up what to do or take opinion polls. No real peers to ask, either. Closest one, was my SIL who had only girls.
I didn't use any particular method, just suggested he sit on the potty and helped him. Got a small potty chair, and put it in the family room. He never used that. It's been a few years (he's almost 14 now) but he was pretty much trained by 30 months or so.
Our daughter (born when my son was almost 3 yrs old) was potty trained for the most part, by her 2nd birthday. She was eager to learn at a young age. I think she was probably 20-22 months when she started. The only FACT I can share is that ON her 2nd birthday, she was wearing cloth training pants (and no diaper or pull-up) when we went to the store to trade her ziploc baggie full of paci's for some toys. She gave up her paci's on her 2nd birthday.
As far as "how to do it right"? Always be positive, never punish or let your frustrations show if they make a mess with it. It is ok to be sad/disappointed, as long as you do so in a supportive way. ("ohhh, we didn't quite make it to the potty in time... sad face. Well, let's get cleaned up. We can try again next time.") Tons of praise for success. Poopy dances and clapping and cheering. Make a big fool of yourself. Kids love that. :)
Good luck.