Tom Huddlestone is 36. Since he is a member of the U21 squad, he pushes the average age of the squad up a lot. However, he only started 4 matches, so he had far less impact on the average age of the team. Nathan Bishop 23, only 5 starts, also boosts the the average age of the squad more than the team, though not to the same extent.
Transfermarkt have the average age of the starting 11 for every match. When Huddlestone started we were older than our opponents, with 3 or 4 exceptions we were younger than the opposition when he didn't. I went through almost all the matches to check.
For the first match of the season the average age of our starting 11 was 18.8, while our opponent's was 19.8, then 18.9 v 19.3, 18.8 v 20.0, 18.5 v 19.5, 18.8 v 19.0, 18.9 v 19.2, 18.7 v 20.6, 18.7 v 19.6, 18.6 v 19.2 and so on. Likewise, if you simply count the number of players aged 20+, we had far fewer than the opposition in the vast majority of matches.
In the recent match against Arsenal, their average age was 19.8, while ours was 20.1, including Huddlestone. There were four 17 year olds in our team, their youngest starter was 18.
Other teams occasionally use older players but they typically belong to the first team squad.