Jones: Leader change 'last thing needed' during Brexit
First Minister Carwyn Jones has said he has given "no thought" to standing down, and there is a "lot of work to do" over the UK leaving the EU.
It has been suggested he would quit before the 2021 assembly election.
But Mr Jones told BBC Wales a change of Welsh Government during Brexit was "the last thing that should happen".
At the party's Welsh conference, Shadow Welsh Secretary Christina Rees praised Labour councils' record, but said May's local elections would be "tough".
She was speaking on the final day of the conference in Llandudno on Sunday.
Speaking from the event, Bridgend AM Mr Jones told the Sunday Politics Wales programme there was a "lot of work to do" over leaving the European Union.
"I just turned 50," he said. "I'm still much younger than Theresa May, younger than David Cameron.
"There's a lot of work to do particularly with Brexit.
"I'm still as enthusiastic as I ever was, and I've given no thought as to when I stand down."
Mr Jones, who became Labour leader in 2009, said: "What I'm absolutely focused on now is delivering the best deal for Brexit.
"The last thing that should happen is for there to be a sudden change in government in Wales or for anywhere else for that matter.
"We need to make sure that people who have been there for a while who've seen what's happened in the past - and I know I'm the longest serving head of government in the UK - then we can get a the point where we have not a hard Brexit, not a soft Brexit, but a sensible Brexit."
The conference later backed a call to formalise Mr Jones's role as Welsh Labour leader, in a vote delayed from Saturday after a problem with voting cards.
Until now, although he has been described as Labour leader in Wales, his official title was leader of the party's assembly group.
Making her first speech to the conference as shadow Welsh secretary, since being appointed by Jeremy Corbyn in February, Ms Rees said she understood how important councillors were.
"You deliver public services in a climate where the UK Tory government has slashed the Welsh Assembly's block grant," she said
"In spite of brutal Tory cuts from Westminster, our Labour councils have a proud record of delivery across Wales.
"Our Welsh Labour government has supported local authorities across the country and each Welsh Labour council has worked hard to maintain vital local services, invest in regeneration, and to provide buildings and facilities that are fit for the future."
Calling the local elections on 4 May "tough" for the party, Ms Rees said she was being "positive" about them.
Labour currently has a majority of 10 of Wales' 22 councils and runs minority administrations in a further two, with Mr Jones admitting it will be difficult to avoid losses.