You're never too old for a denim jacket as long as you wear the sort of clothes that look good with one.
I'm 55 and I have 2. One is a sort of muted purply pink, the other is almost white (probably blue originally and then bleached before it went to the shop, as there is still a bit of blue around the folds and seams) and rather short. That's my favourite one - it looks really good over dresses.
I'm not that keen on classic blue ones any more but I don't think that's got anything to do with my age. I just don't tend to wear much blue (even my jeans are more likely to be black or cream nowadays). If blue suits you, don't hesitate!