While that sounds good, would you think there is a difference between a 20yo and a 30yo in terms of recommendation? Because even for 13yo vs 17yo, that concept would not really work out.
And especially for difficulty, there are games that a 13yo will beat, but a 18yo would not. Reflexes and enthusiasm can be very high at that age.
Hmm. The more I think about it, the more that idea becomes ... not bad, but obsolete. Just look at the retro games. People in their 40s and 50s are (still or again) playing stuff that they played as a 10yo. Concerning age, the only important thing is, if you should not play it, because you are too young for that type of conent. The rest is personal interests and that is done via tagging.
(Ok, there are games for pre-school kids, that even young teens would not touch. So recommended age group, is of course a thing.)