I just had this suggested to me by a train conductor. She didn't believe my child was 4 and said he looked older. She scanned my train ticket and said 'yep, have you got his?'. I offered to find the photos on my phone from when he was bornand show her the date and time stamp and told her she can ask him what age he is. She said 'well I'm just going to have to believe you but it would be useful if you could carry his birth certificate in future'. I think the proof I offered was more than enough. Does anyone else have this problem with kids who are very tall?