There is no such thing as a good age to stretch badly or a bad age to stretch well. I am 41 and stretch after all exercise, should do warm up stretches too but virtually never do. I don't gain a lot of flexibility because of everything else I do that would shorten muscles, but the fact I am not losing is in itself a gain.
I am very careful about how I stretch and focus on the muscles I intend to stretch, if there is no tension there, I am doing it wrong and will be putting undue pressure on joints etc. for no gain at all. There are some very dramatic stretches I have seen people do, calf stretches with their feet in different counties etc. that serve no more useful purpose than a well conceived stretch in a safer position. Check what you are doing and think about the path of the muscle you want to stretch. If you're stretching your quads remember these muscles go from just below hips to knee cap, so a stretch with focus on bend to knee and bit of pressure forward on the hip will be beneficial, having your ankle above your head won't, I have seen it and heard it defended.
Short answer, your age is not the issue. Issue could be form in movement, better option, or potentially injury, not the nice version.
