One of my girls was 20 months before having her first season and it was a full year before she had a second season.We mated her and she missed but ive had a few friends tell me i should get her fertility checked because its likely she could be infertile,is this true?

My youngest had her 1st season @ 22 months......her mother was 17 months, they both went around 9 months between season......youngest has just produced her 1st litter at almost 5 years old, 11 puppies, 10 surviving :-)

One of my girls had her first season at a year old, had to wait 14 months for the second, when she was mated - 11 pups 10 surviving.  Now in season - 14 months again!

I'd suggest that this isn't the case.   I was in touch with the breeder of my Whippet after there was no sign of a season by 11 months (I was waiting on one before spaying - on my vet's advice).   She told me her mother didn't come in until between 15 and 18 months, and neither did her two step sisters (same mother).    None of them was 'infertile'.   But this may also be a 'breed thing' - in other words specific to Whippets.   My own girls usually started at around 8 months, and cycled at that interval too.   Daughters following mum in that.