I don't think you can generalise easily. I started to learn to fly aged 52. Took an IMCR in 15 hours 2 years later and did my IR aged 62. I still fly a TB20 IFR in the airways aged 66 and don't find it difficult. I will agree that I'm not as current on hand flying as I probably should be, but if I'm in doubt I go flying with an instructor to sharpen things up.
I plan carefully and I always strive to keep ahead of the aeroplane, so far so good, but not complacent