Definitely not! My Dad was 23 years older than my Mum - they got married when he was 47 and Mum was 22...! I was born the following year, middle sister the year after and our baby sister (little accident apparently!) was born 10 years later - so Dad was 59 and Mum 34. Both great parents. I remember a few issues about the time Dad retired, when Mum would have been not a lot older than I am now (gulp!) and he died aged 76, when I was 29 and baby sister was 19 and Mum was 52.
However, it would appear to be more socially acceptable for an older guy to be with a youger woman and father kids into his 70s but there's, admittedly gutter press, negative reporting if it's an older woman and a much youger guy.
Anyway, I'm 37 and I'd give my right arm for an energetic 20yo to show a bit of interest in me .
Just a thought... he's not looking for a mother figure or something is he??? How were his parents with him? Also, have a think about 15 years time when you're 53 and he's 35. How long have you been with him? Sorry if I'm being nosey but am genuinely interested - it can work, I've seen it, but as you get older and one person hits middle age and beyond, there may be difficulties. But there's always issues to overcome in any relationship, isn't there - an age gap is just a different type!
I reckon go for it, good luck xx