Should age be just a number?

Should age manner in love? I dated a guy on and off for over two years, when I met him I had determined there was a 4 year age gap, to me it was just perfect! However, two years after meeting I was to discover the age gap was more like 9 years! To say I was in a state of shock was an underestimation. Although annoyed at the deceit I was amazed that I hadn't noticed the difference in our age sooner. That had perplexed me more; I had the misconception that an age gap that great would be more obvious. Then I wondered if age matter? Should it just be a number?
Why is it tradition that the man in the relationship should be older? Last night I bumped into an old flame, we got chatting and he asked me again for my number. He mentioned his age in passing and I nearly passed away! Note I did date this guy a few years ago, and albeit I was aware he was a little younger; I hadn't realised there was an 8 year age gap! He neither looks his age nor acts it. Whilst he was being quizzed by an overbearing male friend of mine, the age question came up, he told my friend to guess his age...an estimate was made of 5 years over...he replied ‘I was born after my time’. So, I thought if maturity levels are the same, should age matter? Does age it matter? Should it not be just a number?