35 is pretty common, though it is the age at which the medical profession categorises you as an older mum - less relevant when not your forst though I believe.
I had mine at 30, 32 and 35 - I have found DC3 hardest, but maybe that's just him
... actually I think its the age gap - the small baby phase wasn't so bed, apart from combining sleep deprivation with a 5 & 3 year old who no longer napped obviously, but the toddler phase is hard when the older ones are no longer toddlers and he has to be stopped from spoiling their games/ homework etc. Its like having 2 kids plus an only sometimes - though other times they do play together or the older ones enjoy looking after him.
I'd look at whether you want to combine older primary age kids with a toddler, more than your age. My older 2 are quite self sufficient in terms of play - I love DC3 desperately but no longer want to play dogs or Playmobile with a toddler some days, though I love his stories and the things he says, I feel too old, at 39, to crawl around the floor with him... I think between them they've aged me at least 10 years though - I feel an old 39 aym! Lots of people are