But of course Lord Cowdrey didn't mean to patronise. Youngster is a perfectly acceptable term among sportsmen for up-and-coming hopefuls, whether humans, horses or dogs. It was the Elizabethans' word for a lively young person, and it was only later that the idea of sparkiness receded and the idea of immaturity took over; Edward Phillips's 1706 dictionary was at the halfway mark when it defined youngster both as "an airy, brisk young man" and "a raw or inexperienced youth".
There is another difficulty though. A youngster is usually thought of as male, so if his lordship wasn't being ageist he was certainly being a bit sexist. Strangely enough, in its early heyday the -ster suffix was meant for a female. A woman dancer in Old English was a hopster, just as a songster was a woman singer and a spinster a woman spinner. The real problem now is that there seems to be no good single word that means a young person of either sex. Youths and lads are male, and neither is entirely satisfactory even for them - youth has a court-room smell, and lads can be any age. Children is hardly right for teenagers these days. Kids was the modish term for all young people in the progressive 1970s, but has dated. I can't imagine its being heard all that often in the House of Lords.