Personally I would not be keen on a (potential) 16 month age gap.
I also don't think (at 35 :o) that 35 is particularly old to be trying for your second child.
If you were 40 I could see the rush.
I think 8 months is very young to have a knackered pregnant mother who doesn't have the energy to enjoy you fully.
Plus the people I know with age gaps below 21 months always seem permanently stressed and exhausted and like they don't enjoy parenthood that much. It seems to me that waiting just a few more months would make your life a lot easier.
But that's all personal experience, anecdote and preference. You will hear from people on here with 13 month gaps that love it.
I imagine people are being negative because they don't want you to make life too difficult for yourself. Being pregnant with your second when your first is a toddler is KNACKERING. Truly.
But you're going to be doing that sooner or later, because I don't suppose you're going to wait much longer no matter what.
If I were you I would listen to what experience parents have to say about this. But just because you listen doesn't mean to have to agree - so consider things like
are they similar in temperament to you? - so if you are very laid back and they are stressy, their experience is not likely to be yours
are they someone who has their own agenda? - i.e. are they your mother? I know my Mum is sometimes overly concerned with my welfare (as she sees it :o)
do they have any insights to offer, even if their main message isn't something you want to take on board?
Also - block out people who are just being negative but with no actual wisdom to offer.
And finally, if all else fails - don't tell people!
If you present them with a done deal they will have to just act delighted. And in fact, they will be.