I'm sorry but I don't get that at all. Yes, perhaps people may feel as if they can't sing hymns that 'high' but it has nothing to do with their voices changing. It's more to do with the fact that people no longer use their singing voices as much as previously.
Of course in times past people had sing-a-longs, more people were members of musical societies, sang in church or were members of church choirs which gave them more opportunity to use their singing voices. And it started from an early age, there was more focus on singing at school - assembly required a hymn and music lessons included singing. Nowadays children are lucky if there is any music programme at school at all. Though I know there has been a rise recently and I do hope this continues.
Pop music also has a lot of effect on this perception, as many pop singers release songs that are rather low, not because singing voices have dropped; more because of the use of close microphones. If you have a mic only 1 inch from your mouth, you need virtually no projection and so you can sing much lower notes than those you can achieve when trying to sing without a mic. People try to imitate this 'pop' sound and technique, so when they try singing hymns in the same way it all seems 'too high'.
At the moment most hymns rarely go above the stave and therefore do not require any true height in the voice. So suggesting that we should look at lowering them seems ridiculous to me. My main complaint about hymn singing at present are two:
- they are too low!
- they are too slow!
Organists tend to play the introduction at one speed and then when the congregation start to sing they play it half speed. I know the thought is that a group sings more slowly than a solo singer, but the organist should keep things moving to ensure the tunes don't grind to a halt. A by-product of this is that with many of the simple tunes in hymns, the quicker they are played the easier they become to sing, because the singers are not then trying to sustain sound over a longer time. Bonus on both points - quicker and easier to sing!
Don't go with the cop out of 'it's too high!', have the commitment to continue singing and with more practice/experience at it, you will be amazed how high you can sing. Voices really haven't changed when speaking in terms of hymn keys, so, say no to low!
Here's the link to Kevin's discussion: