Hi ​amina lifam,

Try,

experience = fields.Char(string='Experience', compute='compute_experience')

@api.depends('join_date')
def compute_experience(self):
    for rec in self:
        if rec.join_date:
            join_date = rec.join_date
            current_date = fields.Date.today()
            years_diff = current_date.year - join_date.year
            months_diff = current_date.month - join_date.month
            if current_date.day < join_date.day:
                months_diff -= 1
            if months_diff < 0:
                years_diff -= 1
                months_diff += 12
            experience_str = '{} years {} months'.format(years_diff, months_diff)
            rec.experience = experience_str
        else:
            rec.experience = 'N/A'

Output:

Hope it helps,
Kiran K